An electrical connector assembly including an electrical connector and a circuit board is provided. The electrical connector has a metallic plate and a plurality of terminals. The metallic plate separates the terminals into two different areas. The metallic plate has a first lateral surface. The circuit board is assembled to the electrical connector. The circuit board has a plurality of pads, a second lateral surface, and top and bottom surfaces opposite to each other. The pads are disposed on the top and bottom surfaces respectively. The second lateral surface is boarded between the top and bottom surfaces. The circuit board further includes at least one grounding circuit exposed from the second lateral surface and facing toward the first lateral surface. The metallic plate is electrically conducted to the grounding circuit by the first lateral surface when the circuit board is assembled to the electrical connector.