diff --git a/.config/example.yml b/.config/example.yml
index e0f768036a..0aa8940677 100644
--- a/.config/example.yml
+++ b/.config/example.yml
@@ -325,10 +325,6 @@ id: 'aidx'
 # To configure them in reverse proxy instead, set this to false.
 #enableIpRateLimit: true
 
-# Enable COOP/COEP headers to make browser contexts cross-origin isolated.
-# This can affect popup opener relationships and cross-origin resource loading.
-#enableCrossOriginIsolation: false
-
 # Number of worker processes
 #clusterLimit: 1
 
diff --git a/.github/misskey/test.yml b/.github/misskey/test.yml
index 842725638a..513bfb1ac0 100644
--- a/.github/misskey/test.yml
+++ b/.github/misskey/test.yml
@@ -4,7 +4,6 @@ setupPassword: example_password_please_change_this_or_you_will_get_hacked
 
 # ローカルでテストするときにポートを被らないようにするためデフォルトのものとは変える(以下同じ)
 port: 61812
-enableCrossOriginIsolation: true
 
 db:
   host: 127.0.0.1
diff --git a/packages/backend/src/config.ts b/packages/backend/src/config.ts
index 9869e9b9a7..d67fe6fc6f 100644
--- a/packages/backend/src/config.ts
+++ b/packages/backend/src/config.ts
@@ -31,7 +31,6 @@ type Source = {
 	chmodSocket?: string;
 	enableIpRateLimit?: boolean;
 	disableHsts?: boolean;
-	enableCrossOriginIsolation?: boolean;
 	db: {
 		host: string;
 		port: number;
@@ -126,7 +125,6 @@ export type Config = {
 	chmodSocket: string | undefined;
 	enableIpRateLimit: boolean;
 	disableHsts: boolean | undefined;
-	enableCrossOriginIsolation: boolean;
 	db: {
 		host: string;
 		port: number;
@@ -290,7 +288,6 @@ export function loadConfig(): Config {
 		chmodSocket: config.chmodSocket,
 		disableHsts: config.disableHsts,
 		enableIpRateLimit: config.enableIpRateLimit ?? true,
-		enableCrossOriginIsolation: config.enableCrossOriginIsolation ?? false,
 		host,
 		hostname,
 		scheme,
diff --git a/packages/backend/src/server/ServerService.ts b/packages/backend/src/server/ServerService.ts
index ba214ebf1b..23ead0feba 100644
--- a/packages/backend/src/server/ServerService.ts
+++ b/packages/backend/src/server/ServerService.ts
@@ -89,14 +89,6 @@ export class ServerService implements OnApplicationShutdown {
 			});
 		}
 
-		if (this.config.enableCrossOriginIsolation) {
-			fastify.addHook('onRequest', (request, reply, done) => {
-				reply.header('Cross-Origin-Opener-Policy', 'same-origin');
-				reply.header('Cross-Origin-Embedder-Policy', 'credentialless');
-				done();
-			});
-		}
-
 		// Register raw-body parser for ActivityPub HTTP signature validation.
 		await fastify.register(fastifyRawBody, {
 			global: false,