Zirconia films were prepared by micro-arc oxidation（MAO） at the applied voltages of 450V in an aqueous solution containing Ca and P.The tribological behaviors of the films were mainly investigated by using ball-on-disc reciprocating friction and wear testing in 25% calf bovine synovia luburication.The results show that MAO zirconia films containing Ca and P are mainly composed of cubic zirconia

tetragonal zirconia and monoclinal zirconia

and the surface of the films exhibits porous structure with a few micro-cracks.Frictional coefficient of MAO films sliding against Si3N4 ceramic ball is lower than that of the untreated Zr-4 alloy

which is attributed to the higher hardness of the films and the less contact area between friction pairs and the micro-pore good for wet lubrication stored a lot of calf bovine synovia.Wear volume of the MAO samples is decreased obviously compared with that of the un-treated Zr-4 alloy

which is the result of higher hardness of the MAO film.The main wear mechanism of Zr-4 alloy is characterized by micro-cutting

while that of the MAO treated Zr-4 alloy is characterized by both fatigue peeling and micro-cutting.