Plasma electrolytic oxidation (PEO) produces oxide ceramic coatings on lightweight Al alloys with high hardness, low thermal conductivity and dimple-like surface morphology. By changing PEO process parameters, coating surface morphology can be manipulated for friction reduction. This study uses both unipolar and bipolar current modes to prepare oxide coatings on Al-Si alloy samples with different durations in order to obtain surface textures with different dimple sizes and densities. The results indicate that decreasing actual contact areas of the coating surfaces and their counterparts lowers the coefficient of friction. The real contact areas, which can be observed in the frequency density distribution histograms and curves of the surface profile data, were different initially and then varied during the sliding tests in progress. More negatively and downwardly shifted maximum values on the probability density distribution function curve of a coating surface profile indicate less real contact area and thus a smaller coefficient of friction. Hardness also plays a factor in frictional behavior.