A mounting apparatus includes a chassis, an expansion member attached to a first end of the expansion card and a mounting tray. The chassis includes a front plate and a rear plate opposite to the front plate. The expansion member is engaged with the rear plate. The mounting tray includes a first section and a second section connected to the first section. A retaining slot is defined in the first section. An engaging portion is disposed on the second section, and a positioning slot defined in the engaging portion. The positioning slot and the retaining slot are located in a longitudinal line. The first section is engaged with the front plate, and the retaining slot and the positioning slot receive a second end of the expansion card.