The authors investigated the wear property of AO (alumina)/AO and SC (silicon carbide)/SC coupling for artificial joint. In the reciprocating motion test, SC/SC shows statistically larger wear rate than AO/AO. The wear rates of both coupling, however, are small enough to be in mild wear stage. Surfaces are polished and maintain smoothness. In addition, SC/SC wear test in O_2rich environment was conducted. When the amount of dissolved oxygen (DO) is high, large wear caused by tribochemical oxidation is observed. But when DO is as low as saturation point under the atmospheric pressure, little wear is observed. As the DO of synovial fluid is lower than saturated, we think the large wear by tribochemical oxidation doesn't occur. From these results, improvement of mechanical wear resistance is important for ceramic/ceramic artificial joint.