diff --git a/backend/router/v1/chat/protocol.py b/backend/router/v1/chat/protocol.py
index 33a7835..74f2081 100644
--- a/backend/router/v1/chat/protocol.py
+++ b/backend/router/v1/chat/protocol.py
@@ -63,6 +63,7 @@ class Res_ChatInit(Res_WebPacketProtocol):
     session_id: str = Field("", description="협상 세션 uuid")
     session_status: int = Field(0, description="세션 상태 코드 (SessionStatus: 1=생성 2=진행중 3=완료 4=미참여 5=거부)")
     quotation_id: str = Field("", description="소속 견적 uuid")
+    qt_number: str = Field("", description="견적번호(EST-...)")
     quotation_end_time: str = Field("", description="견적 마감 시각 (ISO 8601, 타이머용)")
     quotation_memo: str = Field("", description="견적 메모")
     item_id: str = Field("", description="상품 uuid")
diff --git a/backend/services/chat_service.py b/backend/services/chat_service.py
index 6f7691c..0b30355 100644
--- a/backend/services/chat_service.py
+++ b/backend/services/chat_service.py
@@ -238,6 +238,7 @@ class ChatService:
         res.session_id = str(sess.session_id)
         res.session_status = sess.status
         res.quotation_id = str(sess.quotation_id)
+        res.qt_number = sess.qt_number or ""
         res.quotation_end_time = quote.end_time.isoformat(timespec="seconds") if quote.end_time else ""
         res.quotation_memo = quote.memo or ""
         res.item_id = str(item.item_id)
diff --git a/frontend/src/apis/chat/chat.type.ts b/frontend/src/apis/chat/chat.type.ts
index 913f6bd..f3bded6 100644
--- a/frontend/src/apis/chat/chat.type.ts
+++ b/frontend/src/apis/chat/chat.type.ts
@@ -32,6 +32,7 @@ export interface ChatInitResponse {
   session_id: string
   session_status: number
   quotation_id: string
+  qt_number?: string
   quotation_end_time: string
   quotation_memo?: string
   item_id: string
@@ -90,6 +91,7 @@ export function mapInit(r: ChatInitResponse): ChatInitData {
     session_status: r.session_status,
     item_id: r.item_id,
     quotation_id: r.quotation_id,
+    qt_number: r.qt_number ?? '',
     item_name: r.item_name,
     item_code: r.item_code ?? '',
     item_image: r.item_image ?? '',
diff --git a/frontend/src/features/chat/stores/useChatInitStore.ts b/frontend/src/features/chat/stores/useChatInitStore.ts
index 959cc87..ef4b281 100644
--- a/frontend/src/features/chat/stores/useChatInitStore.ts
+++ b/frontend/src/features/chat/stores/useChatInitStore.ts
@@ -16,6 +16,7 @@ const initialState: ChatInitData = {
   session_status: 0,
   item_id: '',
   quotation_id: '',
+  qt_number: '',
   item_name: '',
   item_code: '',
   item_image: '',
diff --git a/frontend/src/features/chat/types.ts b/frontend/src/features/chat/types.ts
index 500fbf9..5dd511a 100644
--- a/frontend/src/features/chat/types.ts
+++ b/frontend/src/features/chat/types.ts
@@ -70,6 +70,7 @@ export type ChatInitData = {
   session_status: number // SessionStatus 코드 (진입 시점 기준)
   item_id: string
   quotation_id: string
+  qt_number: string
   item_name: string
   item_code: string
   item_image: string
diff --git a/frontend/src/pages/ChatPage.tsx b/frontend/src/pages/ChatPage.tsx
index a4c0a25..57ef0e0 100644
--- a/frontend/src/pages/ChatPage.tsx
+++ b/frontend/src/pages/ChatPage.tsx
@@ -2,18 +2,22 @@ import { type ReactNode } from 'react'
 import { useNavigate, useSearchParams, Navigate } from 'react-router'
 import { ArrowLeft, Package, ClipboardList } from 'lucide-react'
 import { cn, interactive } from '@/lib'
+import { Logo } from '@/components'
 import { MainLayout, MainHeaderBar } from '@/layouts'
 import { ChatContainer, ItemSection, RemainingTime } from '@/features/chat'
 import { MobileDrawer } from '@/features/chat/components/MobileDrawer'
 import { MenuSection } from '@/features/chat/components/menu/MenuSection'
 import { useChatUiStore } from '@/features/chat/stores/useChatUiStore'
-import { SidebarFooter } from '@/features/auth'
+import { useChatInitStore } from '@/features/chat/stores/useChatInitStore'
+import { SidebarFooter, usePreLoginBranding } from '@/features/auth'
 
 export function ChatPage() {
   const [searchParams] = useSearchParams()
   const sessionId = searchParams.get('session_id') ?? ''
   const drawer = useChatUiStore((s) => s.drawer)
   const close = useChatUiStore((s) => s.close)
+  const qtNumber = useChatInitStore((s) => s.qt_number)
+  const itemName = useChatInitStore((s) => s.item_name)
 
   // session_id 없이 진입하면 목록으로 되돌린다.
   if (!sessionId) return <Navigate to="/list" replace />
@@ -27,15 +31,21 @@ export function ChatPage() {
           <MainHeaderBar className="px-4 sm:px-6 min-[1180px]:px-8">
             {/* min-w-0: flex 기본 min-width:auto 라 자식이 안 줄어들어 헤더 밖으로 넘치던 것 방지 */}
             <div className="flex w-full min-w-0 items-center justify-between gap-2">
-              <div className="flex min-w-0 shrink items-center gap-2">
+              <div className="flex min-w-0 items-center gap-2">
                 <BackToListButton />
-                <span className="hidden h-4 w-px bg-border lg:inline-block" />
-                <span className="hidden size-2 shrink-0 rounded-full bg-brand-600 animate-pulse lg:inline-block" />
-                <span className="hidden truncate text-sm font-bold text-neutral-90 lg:inline">
-                  실시간 구매 협상 채널
+                <span className="h-4 w-px shrink-0 bg-border" />
+                {/* 헤더 대표값: 협상 중인 상품명 — 여러 협상건 중 '이 건'을 식별하는 기준 */}
+                <span className="min-w-0 truncate text-sm font-bold text-neutral-90">
+                  {itemName || '가격 협상'}
                 </span>
+                {/* 견적번호: 정확한 참조용 보조값. 좁은 모바일에선 숨기고 상품 드로어에서 확인 */}
+                {qtNumber && (
+                  <span className="hidden shrink-0 rounded-md bg-neutral-10 px-2 py-0.5 font-mono text-xs font-bold tracking-tight text-neutral-70 sm:inline-block">
+                    {qtNumber}
+                  </span>
+                )}
               </div>
-              <div className="flex min-w-0 shrink items-center gap-1.5">
+              <div className="flex shrink-0 items-center gap-1.5">
                 <PanelToggle icon={<Package className="size-4" />} label="상품" panel="product" />
                 <PanelToggle icon={<ClipboardList className="size-4" />} label="현황" panel="status" />
                 <RemainingTime />
@@ -49,6 +59,8 @@ export function ChatPage() {
 
       {/* 모바일 드로어 (lg 미만) */}
       <MobileDrawer open={drawer === 'product'} onClose={close} side="left" title="상품 정보">
+        {/* 데스크톱 사이드바 상단(구매사 로고)이 모바일에선 숨으므로, 드로어에서 브랜드+견적번호를 노출 */}
+        <BuyerBrandStrip />
         <ItemSection />
         <SidebarFooter />
       </MobileDrawer>
@@ -72,11 +84,27 @@ function BackToListButton() {
       )}
     >
       <ArrowLeft className="size-4" />
-      <span className="hidden sm:inline">목록으로 돌아가기</span>
+      <span className="hidden sm:inline">목록</span>
     </button>
   )
 }
 
+// 모바일 상품 드로어 상단: 구매사 로고 + 서비스명 + 견적번호(데스크톱 사이드바 상단의 모바일 대체)
+function BuyerBrandStrip() {
+  const branding = usePreLoginBranding()
+  const qtNumber = useChatInitStore((s) => s.qt_number)
+  return (
+    <div className="flex shrink-0 items-center gap-2 border-b border-border px-6 py-3">
+      <Logo logoUrl={branding?.logo_url} serviceName={branding?.service_name} size="sm" />
+      {qtNumber && (
+        <span className="ml-auto shrink-0 rounded-md bg-neutral-10 px-2 py-0.5 font-mono text-xs font-bold tracking-tight text-neutral-70">
+          {qtNumber}
+        </span>
+      )}
+    </div>
+  )
+}
+
 // 헤더 우측: 상품/현황 패널 드로어 토글 (모바일 전용)
 function PanelToggle({
   icon,