A mounting apparatus is provided for mounting a slide rail to a rack post defining a plurality of through holes. The mounting apparatus includes a supporting bracket slidably mounted to the slide rail, and a resilient latch member. The supporting bracket includes an end plate at the front end with two inserting pins extending from a front surface of the end plate and engaged in corresponding through holes of the rack post. The latch member includes a middle plate retained to the supporting bracket, and a latch arm extending forwards. The latch member is operable to be deformed to make the latch arm abut a front surface of the rack post, to prevent the inserting pin from retracting from corresponding through holes.