Many wave energy converters have been developed in the past century with various power takeoff systems, including those devices with air turbines, linear electromagnetic motors, and hydroelectric components. Although these systems have their own advantages, power takeoffs are still recognized as the most important challenge in ocean wave energy technology. In this paper, a mechanical motion rectifier (MMR) based power takeoff system is proposed and prototyped for wave energy converter. This power takeoff system can convert the bidirectional wave motion into unidirectional rotation of generator by integrating two one-way bearings into a rack pinion system. A wave energy converter which contains a 1.2 m buoy and MMR based power takeoff system was designed and fabricated in this paper. The models of power takeoff system and single-body wave energy converter were built and analyzed. The simulation results in regular wave show that MMR based power takeoff can produce more power comparing with linear damping power takeoff system and the optimal PTO damping of MMR system is smaller than that of linear damping system. Lab testing of power takeoff mechanism and ocean testing of the overall ocean wave converter system were also conducted to validate the concept of MMR design. The disengagement and engagement of one-way bearings in the mechanical motion rectifier system were verified in both lab and ocean test.