A fastening device for an expansion card includes a first rack, a second rack opposite to the first rack, and a fastener. The first rack defines a first opening. A supporting plate extends from the first rack toward the second rack. A position tab extends up from the supporting plate. The fastener engages with the first rack and comprises a resilient arm. The supporting plate supports a bottom surface of a first end of the expansion card. The position tab is received in a mounting hole defined in the first end of the expansion card. The resilient arm is deformed and extends through the first opening, and is blocked by the first rack and abuts a top surface of the first end of the expansion card. A second end of the expansion card is fastened to the second rack.