An electrical connector having retaining device comprises a dielectric housing defining a mating face. At least a pair of standoff extend downward from an under face of the housing for mounting on a printed circuit board. The housing defines a longitudinal groove extending along the mating face. A plurality of terminals each has its contacting portion protruding from an inner wall of the groove. Each terminal has its soldering leg extending beyond the under face. A pair of retaining device mount onto the printed circuit board adjacent transverse ends of the housing. The retaining devices jointly define a receiving a receiving slot for an electrical module. Each the retaining device includes a plate portion defining a supporting face and an under face opposite the supporting face. At least a mounting pad extends downward from the under face of the plate portion for mounting on the printed circuit board. A wall portion extends vertically from an edge of the plate portion for guiding the electrical module when the module inserts to the slot. This wall portion also has retaining recess that engages a portion of an inserted electric module. A locking device securely attaching the plate portion to the printed circuit board.