Recently, automotive engines have been operating under harsh conditions of high-power, low viscosity oil and increase of start-stop (e.g. idling stop). In plain bearing used within engine, as oil film thickness decreases, the frequency of direct contacts on the sliding surfaces between the shaft and the bearing are gradually increasing. In fact, the plain bearings for engines would tend to be used under mixed lubrication and the contacts of the surface roughness asperities sometimes occur between the shaft and the bearing. As a result, the bearing wear on the sliding surfaces is accelerated by the contacts of the roughness asperities. In order to predict the bearing performance exactly, it is very important to understand the change progress of the geometric shape of sliding surfaces caused by the wear.Therefore, in this study, to establish the theoretical analysis method of the wear progress of the bearing under mixed lubrication conditions, the following procedures were conducted on a static load: The bearing performance analyses were carried out, based on the mixed lubrication theory which incorporates both the EHL theory with consideration of the surface roughness and the contact theory of the roughness asperities.By the generated contact pressures between the roughness asperities, the wear depth in the bearing surface were calculated, and the wear progress of the bearing sliding surface was analyzed from calculated results.The mixed lubrication analysis involved iteration of above two steps with consideration of the wear progress on the bearing surface.Theoretical analysis results of the wear progress were verified by experiments on the rig tests.