diff --git a/CHANGELOG.md b/CHANGELOG.md
index 09803a0167..69bca97950 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 ### Added
+- Cascade merge: auto-create PRs to downstream branches after merge with configurable rules per repo (#460)
 - Issue status presets: 4 built-in templates (default, software-development, support-tickets, bug-tracking) with API + web UI (#507)
 - Cross-org status migration: copy status definitions from one org to another via API (#507)
 - Auto-create default teams on org creation: Developers (write), Reviewers (read), CI/CD (actions+packages) (#513)
diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index 8fd75de67a..557a1ede75 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -438,6 +438,7 @@ func prepareMigrationTasks() []*migration {
 		newMigration(358, "Add licensing tables (license, entitlement, activation, product_tier)", v1_27.AddLicensingTables),
 		newMigration(359, "Add deploy fields to repo manifest", v1_27.AddDeployFieldsToRepoManifest),
 		newMigration(360, "Add delete allowlist to protected branch", v1_27.AddDeleteAllowlistToProtectedBranch),
+		newMigration(361, "Add cascade merge rule table", v1_27.AddCascadeMergeRuleTable),
 	}
 	return preparedMigrations
 }
diff --git a/models/migrations/v1_27/v362.go b/models/migrations/v1_27/v362.go
new file mode 100644
index 0000000000..03b74339fa
--- /dev/null
+++ b/models/migrations/v1_27/v362.go
@@ -0,0 +1,24 @@
+// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package v1_27
+
+import (
+	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+func AddCascadeMergeRuleTable(x *xorm.Engine) error {
+	type CascadeMergeRule struct {
+		ID           int64              `xorm:"pk autoincr"`
+		RepoID       int64              `xorm:"UNIQUE(s) INDEX NOT NULL"`
+		SourceBranch string             `xorm:"UNIQUE(s) VARCHAR(255) NOT NULL"`
+		TargetBranch string             `xorm:"UNIQUE(s) VARCHAR(255) NOT NULL"`
+		Enabled      bool               `xorm:"NOT NULL DEFAULT true"`
+		AutoMerge    bool               `xorm:"NOT NULL DEFAULT false"`
+		CreatedUnix  timeutil.TimeStamp `xorm:"created"`
+		UpdatedUnix  timeutil.TimeStamp `xorm:"updated"`
+	}
+	return x.Sync(new(CascadeMergeRule))
+}
diff --git a/models/repo/cascade.go b/models/repo/cascade.go
new file mode 100644
index 0000000000..8aa59a6f54
--- /dev/null
+++ b/models/repo/cascade.go
@@ -0,0 +1,63 @@
+// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package repo
+
+import (
+	"context"
+
+	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/models/db"
+	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/timeutil"
+)
+
+type CascadeMergeRule struct {
+	ID           int64              `xorm:"pk autoincr"`
+	RepoID       int64              `xorm:"UNIQUE(s) INDEX NOT NULL"`
+	SourceBranch string             `xorm:"UNIQUE(s) VARCHAR(255) NOT NULL"`
+	TargetBranch string             `xorm:"UNIQUE(s) VARCHAR(255) NOT NULL"`
+	Enabled      bool               `xorm:"NOT NULL DEFAULT true"`
+	AutoMerge    bool               `xorm:"NOT NULL DEFAULT false"`
+	CreatedUnix  timeutil.TimeStamp `xorm:"created"`
+	UpdatedUnix  timeutil.TimeStamp `xorm:"updated"`
+}
+
+func init() {
+	db.RegisterModel(new(CascadeMergeRule))
+}
+
+func GetCascadeRulesByRepoID(ctx context.Context, repoID int64) ([]*CascadeMergeRule, error) {
+	rules := make([]*CascadeMergeRule, 0)
+	return rules, db.GetEngine(ctx).Where("repo_id = ?", repoID).Find(&rules)
+}
+
+func GetCascadeRulesForBranch(ctx context.Context, repoID int64, sourceBranch string) ([]*CascadeMergeRule, error) {
+	rules := make([]*CascadeMergeRule, 0)
+	return rules, db.GetEngine(ctx).Where("repo_id = ? AND source_branch = ? AND enabled = ?", repoID, sourceBranch, true).Find(&rules)
+}
+
+func GetCascadeRuleByID(ctx context.Context, id int64) (*CascadeMergeRule, error) {
+	rule := &CascadeMergeRule{ID: id}
+	has, err := db.GetEngine(ctx).Get(rule)
+	if err != nil {
+		return nil, err
+	}
+	if !has {
+		return nil, nil
+	}
+	return rule, nil
+}
+
+func CreateCascadeRule(ctx context.Context, rule *CascadeMergeRule) error {
+	_, err := db.GetEngine(ctx).Insert(rule)
+	return err
+}
+
+func UpdateCascadeRule(ctx context.Context, rule *CascadeMergeRule) error {
+	_, err := db.GetEngine(ctx).ID(rule.ID).Cols("source_branch", "target_branch", "enabled", "auto_merge").Update(rule)
+	return err
+}
+
+func DeleteCascadeRule(ctx context.Context, repoID, id int64) error {
+	_, err := db.GetEngine(ctx).Where("id = ? AND repo_id = ?", id, repoID).Delete(&CascadeMergeRule{})
+	return err
+}
diff --git a/modules/structs/repo_cascade.go b/modules/structs/repo_cascade.go
new file mode 100644
index 0000000000..aaade87eaf
--- /dev/null
+++ b/modules/structs/repo_cascade.go
@@ -0,0 +1,33 @@
+// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package structs
+
+import "time"
+
+// CascadeMergeRule represents a cascade merge rule
+type CascadeMergeRule struct {
+	ID           int64     `json:"id"`
+	SourceBranch string    `json:"source_branch"`
+	TargetBranch string    `json:"target_branch"`
+	Enabled      bool      `json:"enabled"`
+	AutoMerge    bool      `json:"auto_merge"`
+	CreatedAt    time.Time `json:"created_at"`
+	UpdatedAt    time.Time `json:"updated_at"`
+}
+
+// CreateCascadeMergeRuleOption options for creating a cascade merge rule
+type CreateCascadeMergeRuleOption struct {
+	SourceBranch string `json:"source_branch" binding:"Required"`
+	TargetBranch string `json:"target_branch" binding:"Required"`
+	Enabled      *bool  `json:"enabled"`
+	AutoMerge    *bool  `json:"auto_merge"`
+}
+
+// EditCascadeMergeRuleOption options for editing a cascade merge rule
+type EditCascadeMergeRuleOption struct {
+	SourceBranch *string `json:"source_branch"`
+	TargetBranch *string `json:"target_branch"`
+	Enabled      *bool   `json:"enabled"`
+	AutoMerge    *bool   `json:"auto_merge"`
+}
diff --git a/routers/api/v1/api.go b/routers/api/v1/api.go
index 5967370c6b..9bd32f29b6 100644
--- a/routers/api/v1/api.go
+++ b/routers/api/v1/api.go
@@ -1262,6 +1262,15 @@ func Routes() *web.Router {
 					})
 					m.Post("/priority", bind(api.UpdateBranchProtectionPriories{}), mustNotBeArchived, repo.UpdateBranchProtectionPriories)
 				}, reqToken(), reqAdmin())
+				m.Group("/cascade_rules", func() {
+					m.Get("", repo.ListCascadeRules)
+					m.Post("", mustNotBeArchived, repo.CreateCascadeRule)
+					m.Group("/{id}", func() {
+						m.Get("", repo.GetCascadeRule)
+						m.Patch("", mustNotBeArchived, repo.EditCascadeRule)
+						m.Delete("", mustNotBeArchived, repo.DeleteCascadeRule)
+					})
+				}, reqToken(), reqAdmin())
 				m.Group("/security", func() {
 					m.Get("/alerts", repo.ListSecurityAlerts)
 					m.Get("/alerts/{id}", repo.GetSecurityAlert)
diff --git a/routers/api/v1/repo/cascade.go b/routers/api/v1/repo/cascade.go
new file mode 100644
index 0000000000..e5459ac29a
--- /dev/null
+++ b/routers/api/v1/repo/cascade.go
@@ -0,0 +1,151 @@
+// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package repo
+
+import (
+	"encoding/json"
+	"net/http"
+
+	repo_model "code.mokoconsulting.tech/MokoConsulting/MokoGitea/models/repo"
+	api "code.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/structs"
+	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/context"
+)
+
+func toCascadeRuleAPI(rule *repo_model.CascadeMergeRule) *api.CascadeMergeRule {
+	return &api.CascadeMergeRule{
+		ID:           rule.ID,
+		SourceBranch: rule.SourceBranch,
+		TargetBranch: rule.TargetBranch,
+		Enabled:      rule.Enabled,
+		AutoMerge:    rule.AutoMerge,
+		CreatedAt:    rule.CreatedUnix.AsTime(),
+		UpdatedAt:    rule.UpdatedUnix.AsTime(),
+	}
+}
+
+func ListCascadeRules(ctx *context.APIContext) {
+	rules, err := repo_model.GetCascadeRulesByRepoID(ctx, ctx.Repo.Repository.ID)
+	if err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+	apiRules := make([]*api.CascadeMergeRule, len(rules))
+	for i, rule := range rules {
+		apiRules[i] = toCascadeRuleAPI(rule)
+	}
+	ctx.JSON(http.StatusOK, apiRules)
+}
+
+func CreateCascadeRule(ctx *context.APIContext) {
+	var req api.CreateCascadeMergeRuleOption
+	if err := json.NewDecoder(ctx.Req.Body).Decode(&req); err != nil {
+		ctx.APIError(http.StatusBadRequest, err)
+		return
+	}
+
+	if req.SourceBranch == "" || req.TargetBranch == "" {
+		ctx.APIError(http.StatusUnprocessableEntity, "source_branch and target_branch are required")
+		return
+	}
+
+	if req.SourceBranch == req.TargetBranch {
+		ctx.APIError(http.StatusUnprocessableEntity, "source_branch and target_branch must be different")
+		return
+	}
+
+	rule := &repo_model.CascadeMergeRule{
+		RepoID:       ctx.Repo.Repository.ID,
+		SourceBranch: req.SourceBranch,
+		TargetBranch: req.TargetBranch,
+		Enabled:      true,
+	}
+	if req.Enabled != nil {
+		rule.Enabled = *req.Enabled
+	}
+	if req.AutoMerge != nil {
+		rule.AutoMerge = *req.AutoMerge
+	}
+
+	if err := repo_model.CreateCascadeRule(ctx, rule); err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+
+	ctx.JSON(http.StatusCreated, toCascadeRuleAPI(rule))
+}
+
+func GetCascadeRule(ctx *context.APIContext) {
+	rule, err := repo_model.GetCascadeRuleByID(ctx, ctx.PathParamInt64("id"))
+	if err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+	if rule == nil || rule.RepoID != ctx.Repo.Repository.ID {
+		ctx.APIErrorNotFound()
+		return
+	}
+	ctx.JSON(http.StatusOK, toCascadeRuleAPI(rule))
+}
+
+func EditCascadeRule(ctx *context.APIContext) {
+	rule, err := repo_model.GetCascadeRuleByID(ctx, ctx.PathParamInt64("id"))
+	if err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+	if rule == nil || rule.RepoID != ctx.Repo.Repository.ID {
+		ctx.APIErrorNotFound()
+		return
+	}
+
+	var req api.EditCascadeMergeRuleOption
+	if err := json.NewDecoder(ctx.Req.Body).Decode(&req); err != nil {
+		ctx.APIError(http.StatusBadRequest, err)
+		return
+	}
+
+	if req.SourceBranch != nil {
+		rule.SourceBranch = *req.SourceBranch
+	}
+	if req.TargetBranch != nil {
+		rule.TargetBranch = *req.TargetBranch
+	}
+	if req.Enabled != nil {
+		rule.Enabled = *req.Enabled
+	}
+	if req.AutoMerge != nil {
+		rule.AutoMerge = *req.AutoMerge
+	}
+
+	if rule.SourceBranch == rule.TargetBranch {
+		ctx.APIError(http.StatusUnprocessableEntity, "source_branch and target_branch must be different")
+		return
+	}
+
+	if err := repo_model.UpdateCascadeRule(ctx, rule); err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+
+	ctx.JSON(http.StatusOK, toCascadeRuleAPI(rule))
+}
+
+func DeleteCascadeRule(ctx *context.APIContext) {
+	rule, err := repo_model.GetCascadeRuleByID(ctx, ctx.PathParamInt64("id"))
+	if err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+	if rule == nil || rule.RepoID != ctx.Repo.Repository.ID {
+		ctx.APIErrorNotFound()
+		return
+	}
+
+	if err := repo_model.DeleteCascadeRule(ctx, ctx.Repo.Repository.ID, rule.ID); err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+
+	ctx.Status(http.StatusNoContent)
+}
diff --git a/routers/init.go b/routers/init.go
index a7742cebd4..0b6c0e5916 100644
--- a/routers/init.go
+++ b/routers/init.go
@@ -38,6 +38,7 @@ import (
 	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/auth"
 	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/auth/source/oauth2"
 	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/automerge"
+	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/cascade"
 	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/cron"
 	feed_service "code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/feed"
 	indexer_service "code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/indexer"
@@ -153,6 +154,7 @@ func InitWebInstalled(ctx context.Context) {
 	mustInit(webhook.Init)
 	mustInit(pull_service.Init)
 	mustInit(automerge.Init)
+	cascade.Init()
 	mustInit(task.Init)
 	mustInit(repo_migrations.Init)
 	eventsource.GetManager().Init()
diff --git a/services/cascade/notifier.go b/services/cascade/notifier.go
new file mode 100644
index 0000000000..93a6cdbcff
--- /dev/null
+++ b/services/cascade/notifier.go
@@ -0,0 +1,103 @@
+// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package cascade
+
+import (
+	"context"
+	"fmt"
+
+	issues_model "code.mokoconsulting.tech/MokoConsulting/MokoGitea/models/issues"
+	repo_model "code.mokoconsulting.tech/MokoConsulting/MokoGitea/models/repo"
+	user_model "code.mokoconsulting.tech/MokoConsulting/MokoGitea/models/user"
+	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/log"
+	notify_service "code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/notify"
+	pull_service "code.mokoconsulting.tech/MokoConsulting/MokoGitea/services/pull"
+)
+
+func Init() {
+	notify_service.RegisterNotifier(&cascadeNotifier{})
+}
+
+type cascadeNotifier struct {
+	notify_service.NullNotifier
+}
+
+func (n *cascadeNotifier) MergePullRequest(ctx context.Context, doer *user_model.User, pr *issues_model.PullRequest) {
+	handleCascade(ctx, doer, pr)
+}
+
+func (n *cascadeNotifier) AutoMergePullRequest(ctx context.Context, doer *user_model.User, pr *issues_model.PullRequest) {
+	handleCascade(ctx, doer, pr)
+}
+
+func handleCascade(ctx context.Context, doer *user_model.User, pr *issues_model.PullRequest) {
+	if err := pr.LoadBaseRepo(ctx); err != nil {
+		log.Error("cascade: LoadBaseRepo for PR #%d: %v", pr.Index, err)
+		return
+	}
+
+	rules, err := repo_model.GetCascadeRulesForBranch(ctx, pr.BaseRepo.ID, pr.BaseBranch)
+	if err != nil {
+		log.Error("cascade: GetCascadeRulesForBranch repo=%d branch=%s: %v", pr.BaseRepo.ID, pr.BaseBranch, err)
+		return
+	}
+
+	for _, rule := range rules {
+		if err := createCascadePR(ctx, doer, pr, rule); err != nil {
+			log.Error("cascade: failed to create PR %s→%s in repo %d: %v", rule.SourceBranch, rule.TargetBranch, rule.RepoID, err)
+		}
+	}
+}
+
+func createCascadePR(ctx context.Context, doer *user_model.User, mergedPR *issues_model.PullRequest, rule *repo_model.CascadeMergeRule) error {
+	repo := mergedPR.BaseRepo
+
+	existingPRs, err := issues_model.GetUnmergedPullRequestsByBaseInfo(ctx, repo.ID, rule.TargetBranch)
+	if err != nil {
+		return fmt.Errorf("check existing PRs: %w", err)
+	}
+	for _, existing := range existingPRs {
+		if existing.HeadBranch == rule.SourceBranch && existing.HeadRepoID == repo.ID {
+			log.Info("cascade: PR already exists %s→%s in %s/%s (#%d), skipping",
+				rule.SourceBranch, rule.TargetBranch, repo.OwnerName, repo.Name, existing.Index)
+			return nil
+		}
+	}
+
+	title := fmt.Sprintf("cascade: merge %s into %s", rule.SourceBranch, rule.TargetBranch)
+	body := fmt.Sprintf("Auto-created by cascade merge rule after PR #%d was merged.\n\nSource: `%s` → Target: `%s`",
+		mergedPR.Index, rule.SourceBranch, rule.TargetBranch)
+
+	issue := &issues_model.Issue{
+		RepoID:   repo.ID,
+		Repo:     repo,
+		Title:    title,
+		Content:  body,
+		PosterID: doer.ID,
+		Poster:   doer,
+		IsPull:   true,
+	}
+
+	pullRequest := &issues_model.PullRequest{
+		HeadRepoID: repo.ID,
+		BaseRepoID: repo.ID,
+		HeadBranch: rule.SourceBranch,
+		BaseBranch: rule.TargetBranch,
+		HeadRepo:   repo,
+		BaseRepo:   repo,
+		Type:       issues_model.PullRequestGitea,
+	}
+
+	if err := pull_service.NewPullRequest(ctx, &pull_service.NewPullRequestOptions{
+		Repo:        repo,
+		Issue:       issue,
+		PullRequest: pullRequest,
+	}); err != nil {
+		return fmt.Errorf("NewPullRequest: %w", err)
+	}
+
+	log.Info("cascade: created PR #%d (%s→%s) in %s/%s",
+		issue.Index, rule.SourceBranch, rule.TargetBranch, repo.OwnerName, repo.Name)
+	return nil
+}