An adjustable chair headrest frame includes a headrest provided with a pivotal frame at the rear side. A support frame is pivotally assembled with the pivotal frame of the headrest, having its inner side formed with a recessed face having its outer periphery fixed with plural female-thread studs. An adjusting device is combined at the inside of the support frame, composed of a fit plate, plural stop blocks, a holding plate, springs and a back plate. A combining plate is threadably combined with the fit plate of the adjusting device and assembled at the rear side of a chair. By so designing, the headrest frame can be adjusted upward or downward, and the headrest can be adjusted and positioned at different angles.