A card edge connector assembly for connecting a pair of electrical cards to a printed circuit board includes an upper connector and a lower connector. The upper connector includes a first housing defining a first elongated mating groove along a longitudinal direction with a plurality of first contacts by two sides thereof, and a recess is defined under the first elongated mating groove. The lower connector is moveably received within said recess and includes a second housing defining a second elongated mating groove with a plurality of second contacts by two sides thereof. A metallic member is attached to the upper connector for preventing the lower connector releasing from said recess.