An expansion card mounting apparatus includes a side wall, a support plate, a slot cover, and a retaining member. The side wall defines an expansion card slot. The support plate is connected to the side wall and located above the expansion card slot. The slot cover includes a cover body, a fixing portion extending from the cover body, and a plurality of contact points extending from the cover body. The slot cover covers the expansion card slot with the fixing portion contacting the support plate and the plurality of contact points contacting the side wall. The retaining member includes a main body and a pressing plate connected to the main body. The main body is secured on the side wall. The pressing plate is located on the fixing portion to fix the fixing portion between the pressing plate and the support plate.