Abstract: A board connector includes a first housing including a base and two sidewalls, plural first terminals retained in the base and located between the two sidewalls, and a first metallic shell enclosing the first housing and including a pair of first engaging portions at the sidewalls and a pair of first locking portions located in front of the sidewalls. A cable connector includes a second insulating housing and defining two opposite sides, plural second terminals retained in the second housing, and a second metallic shell enclosing the second housing and including a pair of second locking portions and a pair of second engaging portions behind the second locking portions. The first locking portions are locked with the second engaging portion, and the second locking portion are locked with the first engaging portions after the board connector and the cable connector is mated with each other.