A spindle assembly for magnetic disks of both-end support type has a hub for fixing the disks, a shaft to which the hub is fixed, a pair of bearings which are spaced in vertical or horizontal direction, a pre-loading spring for pre-loading one of the bearings, and a housing composed of housing parts which accommodates the hub, shaft, bearings and the pre-loading spring. The spindle assembly further has an axial reference surface formed on the hub at a right angle with respect to the shaft, and another axial reference surface formed on one of the housing parts at a right angle with respect to the vertical portion of the bearing associated with the one of the housing parts. When the shaft is mounted in the one of the housing parts with the hub and the pre-loading spring fitted therearound, the hub is axially urged by the spring such that the axial reference surface thereon is brought into abutment with the axial reference surface on the one of the housing parts. As a result, the axis of the spindle assembly is determined by the abutment between the reference surfaces and by the bearing in the one of the housing parts. The bearing in the other of the housing parts is axially aligned with the thus determined axis of the spindle assembly.