An electrical connector assembly includes an electrical connector and a metal casing. The electrical connector includes an insulating body and a number of conductive terminals. The insulating body includes a slot. Each conductive terminal includes an abutting portion. The metal casing includes a receiving cavity. When a mating connector is inserted into the receiving cavity and has not yet made contact with the conductive terminals of the electrical connector, a better shielding effect can be achieved. Some of the abutting portions are adapted for electrically connecting with a circuit board, and some of the abutting portions of the conductive terminals are connected with a cable. The metal casing includes a hook portion locking with a lock surface of the circuit board. Therefore, the metal casing can be prevented from detaching from the circuit board in case an external force is applied to pull the cable.