Abstract: A pin on ring test rig was used to investigate the effect of regular concaves on the tribological behavior, with an emphasis place on the effect of the regular concave size on the lubrication behavior. As the results, the surface with appropriately designed regular concave had better lubrication behavior, otherwise, the lubrication behavior would be worsened if the concaves were too large or small. The differences in the tribological behaviors of the smooth and concave surfaces were related to the different real and plastic contact areas. Since the contact area was mainly dependent on the regular concave size, thus it could be feasible to reach better tribological behavior by optimizing the concave size to minimize the plastic contact.