A demountable mounting apparatus for fixing a slide rail to a post includes a mounting bracket secured to the slide rail, a coupling member fixed to the mounting bracket, a latch member rotatably mounted to the mounting bracket, and a restoring member between the latch member and the mounting bracket. The coupling member includes an inserting pin extending into the through hole of the post, and defining a receiving slot. The latch member includes an arm to be received in the receiving slot of the inserting pin, and a hook protruding from the arms. The latch member is locked in a position by the hooks engaging the far surface of the post. A rotation of latch member makes the hooks disengage from the post, thereby allowing the release of the slide rail from the post. The restoring member biases the latch member to the locked position.