diff --git a/src/main/java/gg/agit/konect/domain/chat/repository/ChatRoomMemberRepository.java b/src/main/java/gg/agit/konect/domain/chat/repository/ChatRoomMemberRepository.java
index e2459dd2a..29cc87644 100644
--- a/src/main/java/gg/agit/konect/domain/chat/repository/ChatRoomMemberRepository.java
+++ b/src/main/java/gg/agit/konect/domain/chat/repository/ChatRoomMemberRepository.java
@@ -55,7 +55,7 @@ boolean existsByChatRoomIdAndUserId(
     List<ChatRoomMember> findByChatRoomIds(@Param("chatRoomIds") List<Integer> chatRoomIds);
 
     @Query("""
-        SELECT crm.id.chatRoomId, crm.id.userId
+        SELECT crm.id.chatRoomId, crm.id.userId, crm.createdAt
         FROM ChatRoomMember crm
         WHERE crm.id.chatRoomId IN :chatRoomIds
         """)
diff --git a/src/main/java/gg/agit/konect/domain/chat/service/ChatService.java b/src/main/java/gg/agit/konect/domain/chat/service/ChatService.java
index a1af2b3ba..43d76d479 100644
--- a/src/main/java/gg/agit/konect/domain/chat/service/ChatService.java
+++ b/src/main/java/gg/agit/konect/domain/chat/service/ChatService.java
@@ -206,12 +206,23 @@ private List<ChatRoomSummaryResponse> getDirectChatRooms(Integer userId) {
 
         List<ChatRoomSummaryResponse> roomSummaries = new ArrayList<>();
         List<ChatRoom> personalChatRooms = chatRoomRepository.findByUserId(userId);
-        Map<Integer, List<ChatRoomMember>> roomMembersMap = getRoomMembersMap(personalChatRooms);
+        Map<Integer, List<MemberInfo>> roomMemberInfoMap = getRoomMemberInfoMap(personalChatRooms);
         Map<Integer, Integer> personalUnreadCountMap = getUnreadCountMap(extractChatRoomIds(personalChatRooms), userId);
 
+        List<Integer> allUserIds = roomMemberInfoMap.values().stream()
+            .flatMap(List::stream)
+            .map(MemberInfo::userId)
+            .distinct()
+            .toList();
+
+        Map<Integer, User> userMap = allUserIds.isEmpty()
+            ? Map.of()
+            : userRepository.findAllByIdIn(allUserIds).stream()
+                .collect(Collectors.toMap(User::getId, u -> u));
+
         for (ChatRoom chatRoom : personalChatRooms) {
-            List<ChatRoomMember> members = roomMembersMap.getOrDefault(chatRoom.getId(), List.of());
-            User chatPartner = findDirectPartner(members, user.getId());
+            List<MemberInfo> memberInfos = roomMemberInfoMap.getOrDefault(chatRoom.getId(), List.of());
+            User chatPartner = findDirectPartnerFromMemberInfo(memberInfos, user.getId(), userMap);
             if (chatPartner == null) {
                 continue;
             }
@@ -242,11 +253,12 @@ private List<ChatRoomSummaryResponse> getAdminDirectChatRooms() {
         List<ChatRoomSummaryResponse> roomSummaries = new ArrayList<>();
 
         List<ChatRoom> adminUserRooms = chatRoomRepository.findAllAdminUserDirectRooms(UserRole.ADMIN);
-        Map<Integer, List<Integer>> roomUserIdsMap = getRoomUserIdsMap(adminUserRooms);
+        Map<Integer, List<MemberInfo>> roomMemberInfoMap = getRoomMemberInfoMap(adminUserRooms);
         Map<Integer, Integer> adminUnreadCountMap = getAdminUnreadCountMap(extractChatRoomIds(adminUserRooms));
 
-        List<Integer> allUserIds = roomUserIdsMap.values().stream()
+        List<Integer> allUserIds = roomMemberInfoMap.values().stream()
             .flatMap(List::stream)
+            .map(MemberInfo::userId)
             .distinct()
             .toList();
 
@@ -256,8 +268,8 @@ private List<ChatRoomSummaryResponse> getAdminDirectChatRooms() {
                 .collect(Collectors.toMap(User::getId, user -> user));
 
         for (ChatRoom chatRoom : adminUserRooms) {
-            List<Integer> memberUserIds = roomUserIdsMap.getOrDefault(chatRoom.getId(), List.of());
-            User nonAdminUser = findNonAdminUserFromIds(memberUserIds, userMap);
+            List<MemberInfo> memberInfos = roomMemberInfoMap.getOrDefault(chatRoom.getId(), List.of());
+            User nonAdminUser = findNonAdminUserFromMemberInfo(memberInfos, userMap);
             if (nonAdminUser == null) {
                 continue;
             }
@@ -342,8 +354,16 @@ private ChatMessageDetailResponse sendDirectMessage(
         User sender = userRepository.getById(userId);
         getOrCreateDirectRoomMember(chatRoom, sender);
 
-        List<ChatRoomMember> members = chatRoomMemberRepository.findByChatRoomId(roomId);
-        User receiver = resolveMessageReceiver(sender, members);
+        List<Object[]> memberResults = chatRoomMemberRepository.findRoomMemberIdsByChatRoomIds(List.of(roomId));
+        List<MemberInfo> memberInfos = memberResults.stream()
+            .map(row -> new MemberInfo((Integer)row[1], (LocalDateTime)row[2]))
+            .toList();
+
+        List<Integer> memberUserIds = memberInfos.stream().map(MemberInfo::userId).toList();
+        Map<Integer, User> userMap = userRepository.findAllByIdIn(memberUserIds).stream()
+            .collect(Collectors.toMap(User::getId, u -> u));
+
+        User receiver = resolveMessageReceiverFromMemberInfo(sender, memberInfos, userMap);
 
         ChatMessage chatMessage = chatMessageRepository.save(
             ChatMessage.of(chatRoom, sender, request.content())
@@ -580,8 +600,22 @@ private Integer getMaskedAdminId(User user, ChatRoom chatRoom) {
             return null;
         }
 
-        List<ChatRoomMember> members = chatRoomMemberRepository.findByChatRoomId(chatRoom.getId());
-        User adminUser = findAdminMember(members);
+        List<Object[]> memberResults = chatRoomMemberRepository.findRoomMemberIdsByChatRoomIds(
+            List.of(chatRoom.getId())
+        );
+        List<MemberInfo> memberInfos = memberResults.stream()
+            .map(row -> new MemberInfo((Integer)row[1], (LocalDateTime)row[2]))
+            .toList();
+
+        List<Integer> memberUserIds = memberInfos.stream().map(MemberInfo::userId).toList();
+        if (memberUserIds.isEmpty()) {
+            return null;
+        }
+
+        Map<Integer, User> userMap = userRepository.findAllByIdIn(memberUserIds).stream()
+            .collect(Collectors.toMap(User::getId, u -> u));
+
+        User adminUser = findAdminUserFromMemberInfo(memberInfos, userMap);
         if (adminUser == null) {
             return null;
         }
@@ -700,11 +734,20 @@ private ChatRoomMember getOrCreateDirectRoomMember(ChatRoom chatRoom, User user)
     }
 
     private boolean isAdminUserRoom(ChatRoom chatRoom) {
-        List<ChatRoomMember> members = chatRoomMemberRepository.findByChatRoomId(chatRoom.getId());
-        boolean hasAdmin = members.stream()
-            .anyMatch(m -> m.getUser().getRole() == UserRole.ADMIN);
-        boolean hasNonAdmin = members.stream()
-            .anyMatch(m -> m.getUser().getRole() != UserRole.ADMIN);
+        List<Object[]> memberIds = chatRoomMemberRepository.findRoomMemberIdsByChatRoomIds(
+            List.of(chatRoom.getId())
+        );
+        List<Integer> userIds = memberIds.stream()
+            .map(row -> (Integer)row[1])
+            .toList();
+
+        if (userIds.isEmpty()) {
+            return false;
+        }
+
+        List<User> users = userRepository.findAllByIdIn(userIds);
+        boolean hasAdmin = users.stream().anyMatch(u -> u.getRole() == UserRole.ADMIN);
+        boolean hasNonAdmin = users.stream().anyMatch(u -> u.getRole() != UserRole.ADMIN);
         return hasAdmin && hasNonAdmin;
     }
 
@@ -725,7 +768,10 @@ private Map<Integer, List<ChatRoomMember>> getRoomMembersMap(List<ChatRoom> room
             .collect(Collectors.groupingBy(ChatRoomMember::getChatRoomId));
     }
 
-    private Map<Integer, List<Integer>> getRoomUserIdsMap(List<ChatRoom> rooms) {
+    private record MemberInfo(Integer userId, LocalDateTime createdAt) {
+    }
+
+    private Map<Integer, List<MemberInfo>> getRoomMemberInfoMap(List<ChatRoom> rooms) {
         if (rooms.isEmpty()) {
             return Map.of();
         }
@@ -733,13 +779,15 @@ private Map<Integer, List<Integer>> getRoomUserIdsMap(List<ChatRoom> rooms) {
         List<Integer> roomIds = rooms.stream().map(ChatRoom::getId).toList();
         List<Object[]> results = chatRoomMemberRepository.findRoomMemberIdsByChatRoomIds(roomIds);
 
-        Map<Integer, List<Integer>> roomUserIdsMap = new HashMap<>();
+        Map<Integer, List<MemberInfo>> roomMemberInfoMap = new HashMap<>();
         for (Object[] row : results) {
             Integer chatRoomId = (Integer)row[0];
-            Integer userId = (Integer)row[1];
-            roomUserIdsMap.computeIfAbsent(chatRoomId, k -> new ArrayList<>()).add(userId);
+            Integer memberId = (Integer)row[1];
+            LocalDateTime createdAt = (LocalDateTime)row[2];
+            roomMemberInfoMap.computeIfAbsent(chatRoomId, k -> new ArrayList<>())
+                .add(new MemberInfo(memberId, createdAt));
         }
-        return roomUserIdsMap;
+        return roomMemberInfoMap;
     }
 
     private User findDirectPartner(List<ChatRoomMember> members, Integer userId) {
@@ -750,6 +798,18 @@ private User findDirectPartner(List<ChatRoomMember> members, Integer userId) {
             .orElse(null);
     }
 
+    private User findDirectPartnerFromMemberInfo(
+        List<MemberInfo> memberInfos,
+        Integer userId,
+        Map<Integer, User> userMap
+    ) {
+        return memberInfos.stream()
+            .filter(info -> !info.userId().equals(userId))
+            .min(Comparator.comparing(MemberInfo::createdAt))
+            .map(info -> userMap.get(info.userId()))
+            .orElse(null);
+    }
+
     private User findNonAdminMember(List<ChatRoomMember> members) {
         return members.stream()
             .map(ChatRoomMember::getUser)
@@ -758,15 +818,26 @@ private User findNonAdminMember(List<ChatRoomMember> members) {
             .orElse(null);
     }
 
-    private User findNonAdminUserFromIds(List<Integer> userIds, Map<Integer, User> userMap) {
-        return userIds.stream()
-            .map(userMap::get)
+    private User findNonAdminUserFromMemberInfo(List<MemberInfo> memberInfos, Map<Integer, User> userMap) {
+        return memberInfos.stream()
+            .sorted(Comparator.comparing(MemberInfo::createdAt))
+            .map(info -> userMap.get(info.userId()))
             .filter(Objects::nonNull)
             .filter(user -> user.getRole() != UserRole.ADMIN)
             .findFirst()
             .orElse(null);
     }
 
+    private User findAdminUserFromMemberInfo(List<MemberInfo> memberInfos, Map<Integer, User> userMap) {
+        return memberInfos.stream()
+            .sorted(Comparator.comparing(MemberInfo::createdAt))
+            .map(info -> userMap.get(info.userId()))
+            .filter(Objects::nonNull)
+            .filter(user -> user.getRole() == UserRole.ADMIN)
+            .findFirst()
+            .orElse(null);
+    }
+
     private User findAdminMember(List<ChatRoomMember> members) {
         return members.stream()
             .map(ChatRoomMember::getUser)
@@ -790,4 +861,23 @@ private User resolveMessageReceiver(User sender, List<ChatRoomMember> members) {
         return partner;
     }
 
+    private User resolveMessageReceiverFromMemberInfo(
+        User sender,
+        List<MemberInfo> memberInfos,
+        Map<Integer, User> userMap
+    ) {
+        if (sender.getRole() == UserRole.ADMIN) {
+            User nonAdminUser = findNonAdminUserFromMemberInfo(memberInfos, userMap);
+            if (nonAdminUser != null) {
+                return nonAdminUser;
+            }
+        }
+
+        User partner = findDirectPartnerFromMemberInfo(memberInfos, sender.getId(), userMap);
+        if (partner == null) {
+            throw CustomException.of(FORBIDDEN_CHAT_ROOM_ACCESS);
+        }
+        return partner;
+    }
+
 }