Fluid film lubrication is necessary for sufficient durability of metal on metal total hip prostheses. The radial clearance is an important design factor for fluid film formation. Optimization in size of the clearance, however, requires high level of surface accuracy, including roughness, roundness, and sphericity. In the present study, we made a ball and a cup of Co-Cr-Mo alloy with the surface accuracy as high as possible. The radii of the specimen were 31.985 mm at the cup and 31.948 mm at the ball. The clearance was 18.5 μm. The lubricating ability was evaluated by a friction test using a pendulum machine. The frictional coefficient was measured as the mean 0.143 SD 0.001 under the conditions of the load of 600 N and the lubricant of saline solution. This value was similar to that of polyethylene ball on metal cup of clearance 50 μm but rather higher than that of an alumina/alumina specimen of clearance 17μm.