A hard disk box includes a tray, a cover, and a enclosure. The tray includes a bezel and a bottom plate. The bottom plate includes a locking portion forming a catch. The cover includes a rear wall, and an insert wall extending from a side of the rear wall. A hook extends from the rear wall for engaging the catch of the tray. The enclosure accommodates the bottom plate of the tray and the insert wall of the cover, and is retained between the bezel of the tray and the rear wall of the cover. The enclosure defines an opening in a bottom wall thereof, corresponding to the locking portion of the tray.