Abstract: Plasma electrolytc oxidation (PEO) wear resistant ceramic coating was prepared on TC4 alloy by using the pulsed bipolar power supply. The microstructure, phase composition, friction and wear properties under dry friction and oil lubrication environments as well as failure mechanism under different conditions were studied by using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and a tribometer. It was found that the PEO coating on TC4 alloy was grown mainly by both the oxidation of the substrate and the deposition of electrolyte-borne compounds. The PEO coating greatly improved the wear resistance and decreased the friction coefficient of the material under oil lubrication environment. In non-lubricated environment, the friction force was larger, and the shear stress was the main factor for the failure of the coating. In lubrication environment, the compressive stress was the main factor leading to the failure of coating. Effective lubrication of the PEO coating could improve the wear lifetime of coating greatly.