Abstract: A locking device for an electrical connector is disclosed. The locking device comprises a main plate body defining two first edges and a second edge, a fixing section extending from each of the first edge of the main plate body for fixing into the electrical connector and a boardlock section for locking into a locking hole of a circuit board. The boardlock section includes two resilient arms extending downward from the second edge of the main plate body and defining a gap between the two resilient arms for inward bending thereof, each of the resilient arms having an outer edge defining a curved retention portion, a vertical straight detent portion extending downward from the retention portion, an inward slant pressing portion extending downward from the detent portion at a first slope, and an inward slant guiding portion extending downward from the pressing portion at a second slope larger than the first slope.