A board-to-board connector assembly includes a receptacle connector having a plurality of first terminals, and a plug connector having a plurality of second terminals. Each of the first terminals has two contact portions located oppositely and each of the second terminals has two contact arms located face-to-face. When the plug connector is mated with the receptacle connector, the contact portions of the first terminal are clipped between the contact arms of the corresponding second terminal to electrically contact the corresponding contact arms tightly such that ensures the first terminal and the corresponding second terminal electrically connected with each other steadily.