A hydraulic hinge buffer assembly for a door has a fastening device, a buffering device and a clamping device. The fastening device has a holding mount and a pivot block. The buffering device is mounted in the fastening device and has a pivot pin and a piston element. The pivot pin has an abutting face and at least one holding hook. The piston element is mounted between the holding mount and the pivot pin and has a pushing piston. The pushing piston has a pressing face selectively abutting the abutting face and at least one engaging hook axially formed on and protruding from the pressing face and engaging with the at least one holding hook. The clamping device is connected to the buffering device to rotate relative to the fastening device and has two clamping panels.