Abstract: A hydraulic exerciser includes an elongated hollow support formed with an axial through bore, and a pair of hydraulic cylinders, each of which has a cylinder body and a plug unit which is secured on one end of the cylinder body and which mounts pivotably the cylinder body on a respective one of two ends of the hollow support. The plug unit is formed with a fluid passage for communicating the interior of the cylinder body and the through bore of the hollow support, and includes a first plug member extending sealingly and securely into the cylinder body and having an axial threaded extension which extends out of the cylinder body, and a second plug member having a head section formed with a radial threaded hole which engages threadedly the threaded extension and a shank section extending sealingly and rotatably into the respective one of the two ends of the hollow support.