Abstract: Diamond-like carbon films were deposited on p-Si(100) substrates by a linear anode layer ion beam system using the precursor gas of methane. Effects of the substrate negative bias and the testing environment on the tribological behaviors of the films were considered. Results show that hardness and elastic modulus reached their maximum at the substrate bias of -50 V. When testing in ambient air, films prepared at various substrate bias exhibited good anti-wear property, and there was no significant difference between their tribological behaviors. Also, friction coefficients were very sensitive to the testing environment, mainly as a result of the tribochemical reaction at the tribological interface.