An assembly includes a circuit board, a support perpendicular to the circuit board, and a mounting apparatus including a sliding bracket to accommodate an expansion card, a driving member pivotably mounted to the second support, and a clamping arm mounted to the sliding bracket. The sliding bracket is slidably mounted to the second support, and the driving member is fixed to the sliding bracket. The clamping arm is operable to press or release the expansion card. When the driving member is moved in a first direction, the sliding bracket is moved towards the circuit board, and the expansion card is moved to connect to the circuit board. When the driving member is moved in a second direction opposite to the first direction, the sliding bracket is moved away from the circuit board, and the expansion card disengages from the circuit board.