Abstract: Diamond-like carbon films were successfully deposited on Si substrate by plasma enhanced chemical vapor deposition(PECVD).Friction and wear behaviors of DLC film sliding against a Si3N4 ball at different humidity(5%,20%,40%,60%,80%,and 100%)were measured using a roating-type ball-on-disk tribometer in air. Friction surfaces of the films and Si_3N_4 balls wear were investigated by scanning electron microscope(SEM), and by X-ray photoelectron spectroscopy (XPS). It was found that surface of DLC coating was oxidized by a tribochemical reaction which caused an increase in friction coefficient and wear rate when relative humidity of test environment increased.