diff --git a/src/controllers/friend.controller.js b/src/controllers/friend.controller.js
index 8f54cd1..19a3ec7 100644
--- a/src/controllers/friend.controller.js
+++ b/src/controllers/friend.controller.js
@@ -78,7 +78,7 @@ export const handleGetOutgoingFriendRequests = async (req, res, next) => {
 export const handleAcceptFriendRequest = async (req, res, next) => {
   // 친구 신청 수락 로직 구현
   const receiverUserId = req.user.id;
-  const { requesterUserId } = req.params;
+  const requesterUserId = Number(req.params.requesterUserId);
   userIsNull(receiverUserId, requesterUserId);
   try {
     const result = await acceptFriendRequest(receiverUserId, requesterUserId);
diff --git a/src/repositories/session.repository.js b/src/repositories/session.repository.js
index 25c7ce5..86af207 100644
--- a/src/repositories/session.repository.js
+++ b/src/repositories/session.repository.js
@@ -170,6 +170,19 @@ export const findMatchingSessionBySessionId = async (sessionId) => {
   });
 };
 
+export const findMatchingSessionByParticipantUserId = async (userId, otherUserId) => {
+  const session = await prisma.matchingSession.findFirst({
+    where: {
+      participants: {
+        every: {
+          userId: { in: [userId, otherUserId] },
+        },
+      },
+    },
+  });
+  return session;
+};
+
 export const countMatchingSessionByUserId = async (userId) => {
   const participants = await prisma.sessionParticipant.findMany({
     where: { userId },
diff --git a/src/services/friend.service.js b/src/services/friend.service.js
index 0cc176e..e3a08d6 100644
--- a/src/services/friend.service.js
+++ b/src/services/friend.service.js
@@ -25,6 +25,8 @@ import {
   ConflictError,
   InternalServerError,
 } from "../errors/base.error.js";
+import { findMatchingSessionByParticipantUserId, updateMatchingSessionToFriends, updateMatchingSessionToDiscard } from "../repositories/session.repository.js";
+import { SessionInternalError, SessionNotFoundError } from "../errors/session.error.js";
 
 async function userExistsOrThrow(userId) {
   const userById = await findUserById(userId);
@@ -42,12 +44,12 @@ async function assertUsersExistOrThrow(userId, targetUserId) {
 
   if (!userById)
     throw new InvalidUserError(undefined, "잘못된 유저 정보 입력입니다.", {
-      userId,
+      userId
     });
 
   if (!targetUserById)
     throw new InvalidUserError(undefined, "잘못된 유저 정보 입력입니다.", {
-      targetUserId,
+      targetUserId
     });
 }
 
@@ -178,10 +180,17 @@ export const getOutgoingFriendRequests = async (userId) => {
   }
 };
 
-// 5) 친구 신청 수락
+// 5) 친구 신청 수락 (receiverUserId: userId, requesterUserId: targetUserId)
 export const acceptFriendRequest = async (receiverUserId, requesterUserId) => {
   await assertUsersExistOrThrow(receiverUserId, requesterUserId);
-
+  const session = await findMatchingSessionByParticipantUserId(receiverUserId, requesterUserId);
+  if (!session) { 
+    throw new SessionNotFoundError(undefined, undefined, {receiverUserId, requesterUserId});
+  }
+  const friendsSession = await updateMatchingSessionToFriends(session.id);
+  if(friendsSession.status != "FRIENDS") {
+    throw new SessionInternalError(undefined, "세션 상태 변경에 실패했습니다.", {sessionId: session.id});
+  }
   const req = await userExistsFriendRequest(receiverUserId, requesterUserId);
   if (!req)
     throw new FriendRequestNotFoundError(undefined, undefined, {
@@ -221,7 +230,6 @@ export const acceptFriendRequest = async (receiverUserId, requesterUserId) => {
 // 6) 친구 신청 거절
 export const rejectFriendRequest = async (requesterUserId, receiverUserId) => {
   await assertUsersExistOrThrow(requesterUserId, receiverUserId);
-
   try {
     const rejectedFriendRequest = await updateFriendRequestRejectTx(
       requesterUserId, receiverUserId