A hard disk mounting assembly includes a chassis (10), a first cage (20) mounted to the chassis, a hard disk drive(40) (HDD) and a second cage (60). The HDD defines a plurality of fixing openings (42). The first cage includes a plurality of mounting pillars (28) resilient connected with the cage and received in the fixing openings of the HDD at one end portion. The first cage further defines a pair of engaging apertures (34) at opposite sides thereof. The second cage has a base (62) and two connecting arms (68) depending from the base. the base forms a plurality of elastic fingers (66). The first cage is mounted to the chassis and the HDD is received in the first cage, the second cage hitches the first cage by the connecting arms with the elastic fingers pressing the HDD, thereby mounting the HDD to the chassis.