An expansion card module includes a box, a tray, a circuit board, and an interconnection device. The box is disposed in a drive bay on the front of a case of a computer. The tray is movably installed in the box and has a slide mechanism. The tray slides into or out of the box by the slide mechanism. The circuit board is disposed on the tray and has a first expansion slot. An expansion card electrically inserts into the first expansion slot of the circuit board, and the circuit board is electrically connected to the motherboard of computer through the interconnection device.