An electric connector assembly includes a plug connector and a mating socket connector, and the plug connector includes a base, a tongue plate protruding forwardly from the base and a plurality of electrical contacts. The tongue plate defines two relative surfaces and the tongue plate includes a terminal holder and a side portion beside the terminal holder in a transverse direction. The side portions define at least a pair of clamping portions recessed from the surface of the tongue plate, and the socket connector defines at least a pair of elastic arms for engaging with said clamping portions for enhancing the stability when the electric connector inserted into a mating connector.