A receptacle connector is provided for connection with a plug having two hooks. The receptacle connector includes a first tongue segment, a second tongue segment, and a housing forming an opening and two holes. The first and second tongue segments are disposed in the housing and opposite to each other. The first tongue segment includes a main body, a plurality of first contacts and two stoppers, wherein the two stoppers are located at opposite sides of the contacts and fixed to the main body. When the plug is inserted into the housing through the opening with a normal posture, the hooks are engaged in the holes. When the plug is wrongly inserted into the housing with an inverted posture (upside down), the stoppers obstruct the hooks to prevent insertion of the plug.