The wear characteristics and wear mechanisms of plasma sprayed Al₂ O₃-40%TiO₂ and Cr₂O₃ deposited on casting aluminum alloy(AC4C) were investigated. Specimens were processed for various coating thicknesses. Ball on disk type wear tester was used for wear test. The scratch test on plasma sprayed coating surface showed that critical load to break the coating layer was greater than 40 N. The critical load increase with the increase of coating thickness of specimens. The friction coefficient of Cr₂O₃ coating layer was less than that of Al₂O₃-40%TiO₂ coating layer. The wear resistance of Cr₂O₃ coating layer was greater than that of Al₂O₃-40%TiO₂ coating layer. Microscopic observation of worn surfaces was made by SEM. SEM observation showed that the main mechanism of wear for Al₂O₃-40%TiO₂ coating layer was abrasive wear under 50 N. For the case of Al₂O₃-40%TiO₂ coating layer, as the surface cracks perpendicular to sliding direction propagated, the wear debris was generated in wear track. However, the main mechanism of wear for Cr₂O₃ coating layer was brittle fracture under 150 N.