A mounting apparatus for a slide rail includes a post, a mounting bracket, a fixing plate, and two fasteners. The post longitudinally defines two positioning holes. The mounting bracket is capable of being connected to an end of the slide rail. An end plate is formed on an end of the mounting bracket, and two through holes are defined in the end plate. The fixing plate defines two fixing holes. The fasteners are respectively extended through the positioning holes of the post and the through holes of the end plate, and engaged in the fixing holes of the fixing plate, to allow the fixing plate to be locked to the post. The mounting bracket is transversely slidably coupled to the post and the fixing plate via the two fasteners.