A PTO (power take-off) system for 50kW class rotating body type WEC (wave energy converter) has been designed, constructed and tested. The WEC has a semi-submerged, articulated structure composed of two cylindrical body sections linked together by a hinge joint. The wave-induced motion of the joint is resisted by a hydraulic cylinder, which pumps high-pressure oil to PTO system having a generator-coupled hydraulic motor and a smoothing accumulator. The hydraulic PTO provides an efficient way for generating high quality electric power from the reciprocating motion of the cylinder. The economic viability of a WEC largely depends on the energy conversion efficiency of its PTO. The efficiency of the overall PTO system and individual parts are measured at the 5, 20, 35 and 43kW of generator power while the generator is tied to the commercial 380Vac grid. In this paper, the design of a hydraulic PTO is presented, and the performance of the PTO is discussed.