A riser card module includes a riser card and a mounting rack. The riser card is inserted in a slot of a main board vertically and has a first hook member arranged on the side of the slot. The mounting rack includes an upright board and an engagement member. The upright board mounts the riser card in parallel. The engagement member has a mounted portion, a force portion, and a hook portion. The mounted portion is mounted on the upright board. The force portion and the mounted portion form a predetermined angle. The hook member is connected on the force portion and has a second hook member hooking on the first hook member. When the force portion is pressed toward a direction reducing the predetermined angle, the second hook member is disengaged from the first hook member.