diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index 534850242535..5cc6c629e3ab 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -1642,6 +1642,7 @@ _role:
     gtlAvailable: "グローバルタイムラインの閲覧"
     ltlAvailable: "ローカルタイムラインの閲覧"
     canPublicNote: "パブリック投稿の許可"
+    mentionMax: "ノート内の最大メンション数"
     canInvite: "サーバー招待コードの発行"
     inviteLimit: "招待コードの作成可能数"
     inviteLimitCycle: "招待コードの発行間隔"
diff --git a/packages/backend/src/core/NoteCreateService.ts b/packages/backend/src/core/NoteCreateService.ts
index 9cec614d5c87..3715ed2e93f5 100644
--- a/packages/backend/src/core/NoteCreateService.ts
+++ b/packages/backend/src/core/NoteCreateService.ts
@@ -379,6 +379,10 @@ export class NoteCreateService implements OnApplicationShutdown {
 			}
 		}
 
+		if (mentionedUsers.length > (await this.roleService.getUserPolicies(user.id)).mentionLimit) {
+			throw new Error('Too many mentions');
+		}
+
 		const note = await this.insertNote(user, data, tags, emojis, mentionedUsers);
 
 		setImmediate('post created', { signal: this.#shutdownController.signal }).then(
diff --git a/packages/backend/src/core/RoleService.ts b/packages/backend/src/core/RoleService.ts
index c5baaf3fff42..4c3128411a55 100644
--- a/packages/backend/src/core/RoleService.ts
+++ b/packages/backend/src/core/RoleService.ts
@@ -35,6 +35,7 @@ export type RolePolicies = {
 	gtlAvailable: boolean;
 	ltlAvailable: boolean;
 	canPublicNote: boolean;
+	mentionLimit: number;
 	canInvite: boolean;
 	inviteLimit: number;
 	inviteLimitCycle: number;
@@ -62,6 +63,7 @@ export const DEFAULT_POLICIES: RolePolicies = {
 	gtlAvailable: true,
 	ltlAvailable: true,
 	canPublicNote: true,
+	mentionLimit: 20,
 	canInvite: false,
 	inviteLimit: 0,
 	inviteLimitCycle: 60 * 24 * 7,
@@ -325,6 +327,7 @@ export class RoleService implements OnApplicationShutdown, OnModuleInit {
 			gtlAvailable: calc('gtlAvailable', vs => vs.some(v => v === true)),
 			ltlAvailable: calc('ltlAvailable', vs => vs.some(v => v === true)),
 			canPublicNote: calc('canPublicNote', vs => vs.some(v => v === true)),
+			mentionLimit: calc('mentionLimit', vs => Maht.max(...vs)),
 			canInvite: calc('canInvite', vs => vs.some(v => v === true)),
 			inviteLimit: calc('inviteLimit', vs => Math.max(...vs)),
 			inviteLimitCycle: calc('inviteLimitCycle', vs => Math.max(...vs)),
diff --git a/packages/backend/src/models/json-schema/role.ts b/packages/backend/src/models/json-schema/role.ts
index ef6b279beef3..bb91cfefe09b 100644
--- a/packages/backend/src/models/json-schema/role.ts
+++ b/packages/backend/src/models/json-schema/role.ts
@@ -140,6 +140,10 @@ export const packedRolePoliciesSchema = {
 			type: 'boolean',
 			optional: false, nullable: false,
 		},
+		mentionLimit: {
+			type: 'integer',
+			optional: false, nullable: false,
+		},
 		canInvite: {
 			type: 'boolean',
 			optional: false, nullable: false,
diff --git a/packages/frontend/src/const.ts b/packages/frontend/src/const.ts
index 0bac4d0b7cad..9e41926a97a1 100644
--- a/packages/frontend/src/const.ts
+++ b/packages/frontend/src/const.ts
@@ -75,6 +75,7 @@ export const ROLE_POLICIES = [
 	'gtlAvailable',
 	'ltlAvailable',
 	'canPublicNote',
+	'mentionLimit',
 	'canInvite',
 	'inviteLimit',
 	'inviteLimitCycle',
diff --git a/packages/frontend/src/pages/admin/roles.editor.vue b/packages/frontend/src/pages/admin/roles.editor.vue
index ad9df35dbf26..eb8a59b34f48 100644
--- a/packages/frontend/src/pages/admin/roles.editor.vue
+++ b/packages/frontend/src/pages/admin/roles.editor.vue
@@ -160,6 +160,25 @@ SPDX-License-Identifier: AGPL-3.0-only
 				</div>
 			</MkFolder>
 
+			<MkFolder v-if="matchQuery([i18n.ts._role._options.mentionMax, 'mentionLimit'])">
+				<template #label>{{ i18n.ts._role._options.mentionMax }}</template>
+				<template #suffix>
+					<span v-if="role.policies.mentionLimit.useDefault" :class="$style.useDefaultLabel">{{ i18n.ts._role.useBaseValue }}</span>
+					<span v-else>{{ role.policies.mentionLimit.value }}</span>
+					<span :class="$style.priorityIndicator"><i :class="getPriorityIcon(role.policies.mentionLimit)"></i></span>
+				</template>
+				<div class="_gaps">
+					<MkSwitch v-model="role.policies.mentionLimit.useDefault" :readonly="readonly">
+						<template #label>{{ i18n.ts._role.useBaseValue }}</template>
+					</MkSwitch>
+					<MkInput v-model="role.policies.mentionLimit.value" :disabled="role.policies.mentionLimit.useDefault" type="number" :readonly="readonly">
+					</MkInput>
+					<MkRange v-model="role.policies.mentionLimit.priority" :min="0" :max="2" :step="1" easing :textConverter="(v) => v === 0 ? i18n.ts._role._priority.low : v === 1 ? i18n.ts._role._priority.middle : v === 2 ? i18n.ts._role._priority.high : ''">
+						<template #label>{{ i18n.ts._role.priority }}</template>
+					</MkRange>
+				</div>
+			</MkFolder>
+
 			<MkFolder v-if="matchQuery([i18n.ts._role._options.canInvite, 'canInvite'])">
 				<template #label>{{ i18n.ts._role._options.canInvite }}</template>
 				<template #suffix>
diff --git a/packages/frontend/src/pages/admin/roles.vue b/packages/frontend/src/pages/admin/roles.vue
index 496cb096645f..9753d9f6cb7a 100644
--- a/packages/frontend/src/pages/admin/roles.vue
+++ b/packages/frontend/src/pages/admin/roles.vue
@@ -48,6 +48,13 @@ SPDX-License-Identifier: AGPL-3.0-only
 							</MkSwitch>
 						</MkFolder>
 
+						<MkFolder v-if="matchQuery([i18n.ts._role._options.mentionMax, 'mentionLimit'])">
+							<template #label>{{ i18n.ts._role._options.mentionMax }}</template>
+							<template #suffix>{{ policies.mentionLimit }}</template>
+							<MkInput v-model="policies.mentionLimit" type="number">
+							</MkInput>
+						</MkFolder>
+
 						<MkFolder v-if="matchQuery([i18n.ts._role._options.canInvite, 'canInvite'])">
 							<template #label>{{ i18n.ts._role._options.canInvite }}</template>
 							<template #suffix>{{ policies.canInvite ? i18n.ts.yes : i18n.ts.no }}</template>
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index ad3a9a7c661b..4b0aa3fbfffc 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -4631,6 +4631,7 @@ export type components = {
       gtlAvailable: boolean;
       ltlAvailable: boolean;
       canPublicNote: boolean;
+      mentionLimit: number;
       canInvite: boolean;
       inviteLimit: number;
       inviteLimitCycle: number;