A fastening device for an expansion card includes a first rack located at a front side, a second rack located at a rear side, a supporting member fastened to the first rack, and a rotating member rotatably connected to the supporting member. A pole extends up from the supporting member. When the rotating member is rotated up, a first end of the expansion card is operable to abut a top of the supporting member and the pole extends through a mounting hole defined in the first end of the expansion card. The rotating member is operable to rotate down to abut a top of the expansion card and engage with the supporting member. A second end of the expansion card opposite to the first end is fastened to the second rack.