A disk chuck which centers and clamps data storage disks during a disk formatting process. The disk chuck is designed to clamp or unclamp the disks at the same time. The disk chuck includes a hollow main shaft which orderly fits and seats the disks thereon and a piston which is situated in the hollow main shaft so as to axially move in the hollow main shaft in opposite directions. A clamping shaft is axially received in the hollow main shaft and coupled to the piston so as to move along with the piston in the same direction to clamp or unclamp the disks seated on the hollow main shaft. An upper end of the clamping shaft having a disk clamping part extends to project beyond an upper end of the hollow main shaft.