diff --git a/packages/backend/src/core/AnnouncementService.ts b/packages/backend/src/core/AnnouncementService.ts
index 394b47c99..07a8a7833 100644
--- a/packages/backend/src/core/AnnouncementService.ts
+++ b/packages/backend/src/core/AnnouncementService.ts
@@ -138,7 +138,7 @@ export class AnnouncementService {
 		limit: number,
 		offset: number,
 		moderator: MiUser,
-	): Promise<(MiAnnouncement & { userInfo: Packed<'UserLite'> | null, reads: number })[]> {
+	): Promise<(MiAnnouncement & { userInfo: Packed<'UserLite'> | null, reads: number, lastReadAt: Date | null })[]> {
 		const query = this.announcementsRepository.createQueryBuilder('announcement');
 
 		if (userId) {
@@ -157,13 +157,14 @@ export class AnnouncementService {
 			.offset(offset)
 			.getMany();
 
-		const reads = new Map<MiAnnouncement, number>();
-
-		for (const announcement of announcements) {
-			reads.set(announcement, await this.announcementReadsRepository.countBy({
-				announcementId: announcement.id,
-			}));
-		}
+		const reads = announcements.length > 0
+			? await this.announcementReadsRepository.createQueryBuilder()
+				.select('"announcementId", count(*) as "reads", max("id") as "lastReadId"')
+				.where('"announcementId" IN (:...announcementIds)', { announcementIds: announcements.map(a => a.id) })
+				.groupBy('"announcementId"')
+				.getRawMany<{ announcementId: string, reads: number, lastReadId: string | null }>()
+				.then(rs => new Map(rs.map(r => [r.announcementId, { reads: r.reads, lastReadAt: r.lastReadId ? this.idService.parse(r.lastReadId).date : null }])))
+			: new Map();
 
 		const users = await this.usersRepository.findBy({
 			id: In(announcements.map(a => a.userId).filter(id => id != null)),
@@ -174,8 +175,8 @@ export class AnnouncementService {
 
 		return announcements.map(announcement => ({
 			...announcement,
+			...reads.get(announcement.id) ?? { reads: 0, lastReadAt: null },
 			userInfo: packedUsers.find(u => u.id === announcement.userId) ?? null,
-			reads: reads.get(announcement) ?? 0,
 		}));
 	}
 
@@ -293,18 +294,20 @@ export class AnnouncementService {
 				'read.id IS NOT NULL as "isRead"',
 			]);
 			query
-				.andWhere(
-					new Brackets((qb) => {
-						qb.orWhere('announcement."userId" = :userId', { userId: me.id });
-						qb.orWhere('announcement."userId" IS NULL');
-					}),
-				)
-				.andWhere(
-					new Brackets((qb) => {
-						qb.orWhere('announcement."forExistingUsers" = false');
-						qb.orWhere('announcement.id > :userId', { userId: me.id });
-					}),
-				);
+				.andWhere(new Brackets((qb) => {
+					qb.orWhere(new Brackets((nqb) => {
+						nqb.andWhere('announcement."userId" = :userId', { userId: me.id });
+						nqb.andWhere(isActive ? 'read.id IS NULL' : 'read.id IS NOT NULL');
+					}));
+					qb.orWhere(new Brackets((nqb) => {
+						nqb.andWhere('announcement."userId" IS NULL');
+						nqb.andWhere('announcement."isActive" = :isActive', { isActive });
+					}));
+				}))
+				.andWhere(new Brackets((qb) => {
+					qb.orWhere('announcement."forExistingUsers" = false');
+					qb.orWhere('announcement.id > :userId', { userId: me.id });
+				}));
 		} else {
 			query.select([
 				'announcement.*',
@@ -312,12 +315,9 @@ export class AnnouncementService {
 			]);
 			query.andWhere('announcement."userId" IS NULL');
 			query.andWhere('announcement."forExistingUsers" = false');
+			query.andWhere('announcement."isActive" = :isActive', { isActive });
 		}
 
-		query.andWhere('announcement."isActive" = :isActive', {
-			isActive: isActive,
-		});
-
 		if (isActive) {
 			query.orderBy({
 				'"isRead"': 'ASC',
diff --git a/packages/backend/src/server/api/endpoints/admin/announcements/list.ts b/packages/backend/src/server/api/endpoints/admin/announcements/list.ts
index c8719ffb8..573652ac5 100644
--- a/packages/backend/src/server/api/endpoints/admin/announcements/list.ts
+++ b/packages/backend/src/server/api/endpoints/admin/announcements/list.ts
@@ -97,6 +97,11 @@ export const meta = {
 					type: 'number',
 					optional: false, nullable: false,
 				},
+				lastReadAt: {
+					type: 'string',
+					optional: false, nullable: true,
+					format: 'date-time',
+				},
 			},
 		},
 	},
@@ -140,6 +145,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				userId: announcement.userId,
 				user: announcement.userInfo,
 				reads: announcement.reads,
+				lastReadAt: announcement.lastReadAt?.toISOString() ?? null,
 			}));
 		});
 	}
diff --git a/packages/frontend/src/components/MkUserAnnouncementEditDialog.vue b/packages/frontend/src/components/MkUserAnnouncementEditDialog.vue
index ec46dac34..7fee7c1b1 100644
--- a/packages/frontend/src/components/MkUserAnnouncementEditDialog.vue
+++ b/packages/frontend/src/components/MkUserAnnouncementEditDialog.vue
@@ -53,7 +53,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 					{{ i18n.ts._announcement.silence }}
 					<template #caption>{{ i18n.ts._announcement.silenceDescription }}</template>
 				</MkSwitch>
-				<p v-if="reads">{{ i18n.tsx.nUsersRead({ n: reads }) }}</p>
+				<p v-if="reads">{{ i18n.tsx.nUsersRead({ n: reads }) }} <span v-if="lastReadAt">(<MkTime :time="lastReadAt" mode="absolute"/>)</span></p>
 				<MkUserCardMini v-if="props.user.id" :user="props.user"></MkUserCardMini>
 				<MkButton v-if="announcement" danger @click="del()"><i class="ti ti-trash"></i> {{ i18n.ts.delete }}</MkButton>
 			</div>
@@ -94,6 +94,7 @@ const closeDuration = ref<number>(props.announcement ? props.announcement.closeD
 const displayOrder = ref<number>(props.announcement ? props.announcement.displayOrder : 0);
 const silence = ref<boolean>(props.announcement ? props.announcement.silence : false);
 const reads = ref<number>(props.announcement ? props.announcement.reads : 0);
+const lastReadAt = ref<string | null>(props.announcement ? props.announcement.lastReadAt : null);
 
 const emit = defineEmits<{
 	(ev: 'done', v: { deleted?: boolean; updated?: any; created?: any }): void,
diff --git a/packages/frontend/src/pages/admin-user.vue b/packages/frontend/src/pages/admin-user.vue
index 3a9a6c775..4f339e550 100644
--- a/packages/frontend/src/pages/admin-user.vue
+++ b/packages/frontend/src/pages/admin-user.vue
@@ -149,7 +149,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 									<i v-else-if="announcement.icon === 'success'" class="ti ti-check" style="color: var(--success);"></i>
 								</span>
 								<span>{{ announcement.title }}</span>
-								<span v-if="announcement.reads > 0" style="margin-left: auto; opacity: 0.7;">{{ i18n.ts.messageRead }}</span>
+								<span v-if="announcement.reads > 0" style="margin-left: auto; opacity: 0.7;">{{ i18n.ts.messageRead }} <span v-if="announcement.lastReadAt">(<MkTime :time="announcement.lastReadAt" mode="absolute"/>)</span></span>
 							</div>
 						</div>
 					</template>
diff --git a/packages/frontend/src/pages/admin/announcements.vue b/packages/frontend/src/pages/admin/announcements.vue
index afd97bc06..7a0f12844 100644
--- a/packages/frontend/src/pages/admin/announcements.vue
+++ b/packages/frontend/src/pages/admin/announcements.vue
@@ -76,7 +76,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 					<MkSwitch v-model="announcement.silence" :helpText="i18n.ts._announcement.silenceDescription">
 						{{ i18n.ts._announcement.silence }}
 					</MkSwitch>
-					<p v-if="announcement.reads">{{ i18n.tsx.nUsersRead({ n: announcement.reads }) }}</p>
+					<p v-if="announcement.reads">{{ i18n.tsx.nUsersRead({ n: announcement.reads }) }} <span v-if="announcement.lastReadAt">(<MkTime :time="announcement.lastReadAt" mode="absolute"/>)</span></p>
 					<MkUserCardMini v-if="announcement.userId" :user="announcement.user" @click="editUser(announcement)"></MkUserCardMini>
 					<MkButton v-else class="button" inline primary @click="editUser(announcement)">{{ i18n.ts.specifyUser }}</MkButton>
 					<div class="buttons _buttons">
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 92b3b7769..ae000aca0 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -6183,6 +6183,8 @@ export type operations = {
               userId: string | null;
               user: components['schemas']['UserLite'] | null;
               reads: number;
+              /** Format: date-time */
+              lastReadAt: string | null;
             })[];
         };
       };