A disk drive mounting device for use in an electronic apparatus includes a mounting frame, fasteners, and a cover member. The mounting frame includes a mounting plate, a flange formed at a side of the mounting plate, and a plurality of mounting ears extending outwardly from the mounting plate. Each of the mounting ears defines at least one receiving cutout therein. In use, one end of each of the fasteners is mounted on the disk drive and the other end is received in the receiving cutout of a corresponding mounting ear. The cover member is secured on the flange of the mounting frame and abuts the at least one disk drive to prevent the fasteners from disengaging from the receiving cutouts of the mounting ears. A disk drive assembly is also provided.