diff --git a/internal/database/conversation.go b/internal/database/conversation.go
index cf2d59d8..7a769656 100644
--- a/internal/database/conversation.go
+++ b/internal/database/conversation.go
@@ -13,6 +13,9 @@ import (
 	"go.uber.org/zap"
 )
 
+// ProjectFilterUnbound 列表 API 中 project_id=__none__ 表示仅未绑定项目的对话。
+const ProjectFilterUnbound = "__none__"
+
 // Conversation 对话
 type Conversation struct {
 	ID        string    `json:"id"`
@@ -361,20 +364,44 @@ func (db *DB) GetConversationLite(id string) (*Conversation, error) {
 	return &conv, nil
 }
 
+func conversationProjectIDColumn(alias string) string {
+	if alias != "" {
+		return alias + ".project_id"
+	}
+	return "project_id"
+}
+
+func appendConversationProjectFilter(where string, args []interface{}, projectID, alias string) (string, []interface{}) {
+	pid := strings.TrimSpace(projectID)
+	if pid == "" {
+		return where, args
+	}
+	col := conversationProjectIDColumn(alias)
+	if pid == ProjectFilterUnbound {
+		return where + fmt.Sprintf(" AND (%s IS NULL OR TRIM(COALESCE(%s, '')) = '')", col, col), args
+	}
+	return where + fmt.Sprintf(" AND %s = ?", col), append(args, pid)
+}
+
 // CountConversations 统计对话数量。
-func (db *DB) CountConversations(search string) (int, error) {
+func (db *DB) CountConversations(search, projectID string) (int, error) {
 	var count int
 	var err error
 	if search != "" {
 		searchPattern := "%" + search + "%"
-		err = db.QueryRow(
-			`SELECT COUNT(*) FROM conversations c
-			 WHERE c.title LIKE ?
-			    OR EXISTS (SELECT 1 FROM messages m WHERE m.conversation_id = c.id AND m.content LIKE ?)`,
-			searchPattern, searchPattern,
-		).Scan(&count)
+		where := ` WHERE (c.title LIKE ?
+			    OR EXISTS (SELECT 1 FROM messages m WHERE m.conversation_id = c.id AND m.content LIKE ?))`
+		args := []interface{}{searchPattern, searchPattern}
+		where, args = appendConversationProjectFilter(where, args, projectID, "c")
+		err = db.QueryRow(`SELECT COUNT(*) FROM conversations c`+where, args...).Scan(&count)
 	} else {
-		err = db.QueryRow(`SELECT COUNT(*) FROM conversations`).Scan(&count)
+		where := ""
+		args := []interface{}{}
+		where, args = appendConversationProjectFilter(where, args, projectID, "")
+		if where != "" {
+			where = " WHERE" + strings.TrimPrefix(where, " AND")
+		}
+		err = db.QueryRow(`SELECT COUNT(*) FROM conversations`+where, args...).Scan(&count)
 	}
 	if err != nil {
 		return 0, fmt.Errorf("统计对话失败: %w", err)
@@ -395,7 +422,7 @@ func conversationOrderClause(sortBy, tableAlias string) string {
 }
 
 // ListConversations 列出所有对话
-func (db *DB) ListConversations(limit, offset int, search, sortBy string) ([]*Conversation, error) {
+func (db *DB) ListConversations(limit, offset int, search, sortBy, projectID string) ([]*Conversation, error) {
 	var rows *sql.Rows
 	var err error
 
@@ -403,20 +430,30 @@ func (db *DB) ListConversations(limit, offset int, search, sortBy string) ([]*Co
 		// 使用 EXISTS 子查询代替 LEFT JOIN + DISTINCT，避免大表笛卡尔积
 		searchPattern := "%" + search + "%"
 		orderClause := conversationOrderClause(sortBy, "c")
+		where := ` WHERE (c.title LIKE ?
+			    OR EXISTS (SELECT 1 FROM messages m WHERE m.conversation_id = c.id AND m.content LIKE ?))`
+		args := []interface{}{searchPattern, searchPattern}
+		where, args = appendConversationProjectFilter(where, args, projectID, "c")
+		args = append(args, limit, offset)
 		rows, err = db.Query(
 			`SELECT c.id, c.title, COALESCE(c.pinned, 0), c.created_at, c.updated_at, c.project_id
-			 FROM conversations c
-			 WHERE c.title LIKE ?
-			    OR EXISTS (SELECT 1 FROM messages m WHERE m.conversation_id = c.id AND m.content LIKE ?)
+			 FROM conversations c`+where+`
 			 `+orderClause+`
 			 LIMIT ? OFFSET ?`,
-			searchPattern, searchPattern, limit, offset,
+			args...,
 		)
 	} else {
 		orderClause := conversationOrderClause(sortBy, "")
+		where := ""
+		args := []interface{}{}
+		where, args = appendConversationProjectFilter(where, args, projectID, "")
+		if where != "" {
+			where = " WHERE" + strings.TrimPrefix(where, " AND")
+		}
+		args = append(args, limit, offset)
 		rows, err = db.Query(
-			"SELECT id, title, COALESCE(pinned, 0), created_at, updated_at, project_id FROM conversations "+orderClause+" LIMIT ? OFFSET ?",
-			limit, offset,
+			"SELECT id, title, COALESCE(pinned, 0), created_at, updated_at, project_id FROM conversations"+where+" "+orderClause+" LIMIT ? OFFSET ?",
+			args...,
 		)
 	}
 
@@ -472,23 +509,30 @@ const ungroupedConversationsSQL = `
 	)`
 
 // CountUngroupedConversations 统计不在任何分组中的对话数量。
-func (db *DB) CountUngroupedConversations() (int, error) {
+func (db *DB) CountUngroupedConversations(projectID string) (int, error) {
+	where := ungroupedConversationsSQL
+	args := []interface{}{}
+	where, args = appendConversationProjectFilter(where, args, projectID, "c")
 	var count int
-	if err := db.QueryRow(`SELECT COUNT(*) ` + ungroupedConversationsSQL).Scan(&count); err != nil {
+	if err := db.QueryRow(`SELECT COUNT(*) `+where, args...).Scan(&count); err != nil {
 		return 0, fmt.Errorf("统计未分组对话失败: %w", err)
 	}
 	return count, nil
 }
 
 // ListUngroupedConversations 列出不在任何分组中的对话（最近对话侧栏）。
-func (db *DB) ListUngroupedConversations(limit, offset int, sortBy string) ([]*Conversation, error) {
+func (db *DB) ListUngroupedConversations(limit, offset int, sortBy, projectID string) ([]*Conversation, error) {
 	orderClause := conversationOrderClause(sortBy, "c")
+	where := ungroupedConversationsSQL
+	args := []interface{}{}
+	where, args = appendConversationProjectFilter(where, args, projectID, "c")
+	args = append(args, limit, offset)
 	rows, err := db.Query(
 		`SELECT c.id, c.title, COALESCE(c.pinned, 0), c.created_at, c.updated_at, c.project_id `+
-			ungroupedConversationsSQL+`
+			where+`
 		 `+orderClause+`
 		 LIMIT ? OFFSET ?`,
-		limit, offset,
+		args...,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("查询未分组对话失败: %w", err)
diff --git a/internal/database/conversation_project_filter_test.go b/internal/database/conversation_project_filter_test.go
new file mode 100644
index 00000000..457542b7
--- /dev/null
+++ b/internal/database/conversation_project_filter_test.go
@@ -0,0 +1,60 @@
+package database
+
+import (
+	"path/filepath"
+	"testing"
+
+	"go.uber.org/zap"
+)
+
+func TestConversationProjectFilter(t *testing.T) {
+	tmp := t.TempDir()
+	dbPath := filepath.Join(tmp, "conversations.db")
+	db, err := NewDB(dbPath, zap.NewNop())
+	if err != nil {
+		t.Fatalf("NewDB: %v", err)
+	}
+	defer db.Close()
+
+	p, err := db.CreateProject(&Project{Name: "target-a", Status: "active"})
+	if err != nil {
+		t.Fatalf("CreateProject: %v", err)
+	}
+
+	convNone, err := db.CreateConversation("unbound", ConversationCreateMeta{})
+	if err != nil {
+		t.Fatalf("CreateConversation unbound: %v", err)
+	}
+	convBound, err := db.CreateConversation("bound", ConversationCreateMeta{ProjectID: p.ID})
+	if err != nil {
+		t.Fatalf("CreateConversation bound: %v", err)
+	}
+
+	totalAll, err := db.CountConversations("", "")
+	if err != nil || totalAll < 2 {
+		t.Fatalf("CountConversations all: total=%d err=%v", totalAll, err)
+	}
+
+	totalBound, err := db.CountConversations("", p.ID)
+	if err != nil || totalBound != 1 {
+		t.Fatalf("CountConversations project: total=%d err=%v", totalBound, err)
+	}
+
+	totalUnbound, err := db.CountConversations("", ProjectFilterUnbound)
+	if err != nil || totalUnbound != 1 {
+		t.Fatalf("CountConversations unbound: total=%d err=%v", totalUnbound, err)
+	}
+
+	listBound, err := db.ListConversations(10, 0, "", "", p.ID)
+	if err != nil || len(listBound) != 1 || listBound[0].ID != convBound.ID {
+		t.Fatalf("ListConversations project: %+v err=%v", listBound, err)
+	}
+
+	listUnbound, err := db.ListConversations(10, 0, "", "", ProjectFilterUnbound)
+	if err != nil || len(listUnbound) != 1 || listUnbound[0].ID != convNone.ID {
+		t.Fatalf("ListConversations unbound: %+v err=%v", listUnbound, err)
+	}
+
+	_ = convNone
+	_ = convBound
+}