A positioning structure for a removable hard drive includes an enclosure and a tray. The enclosure is used for being mounted by the hard drive, and disposed with a plurality of positioning holes. The tray includes a bottom and two side walls vertically extending therefrom. A space being is formed by the bottom and the side walls. The bottom is formed with a plurality of positioning pillars corresponding to the positioning holes. The enclosure is received in the space, and the positioning holes are correspondingly inserted by the positioning pillars.