A card edge connector for mating with an electronic card includes an elongated housing, a number of contacts and a retainer disposed in the housing. The housing has a center slot extending along a lengthwise direction of the housing and a first tower section at one end thereof. The retainer is rotatably retained in the first tower section and does not extend beyond the first tower along the lengthwise direction, a thickness direction of the housing and a direction opposite to an insertion direction of the electronic card. The retainer has a locker to lock the electronic card and at least a spring sandwiched between the locker and an outer wall of the first tower section to make the locker automatically move in the lengthwise direction in an insertion process of the electronic card.