Abstract: A series of Al doped diamond-like carbon films were deposited on N (100) Si substrates by radio frequency magnetron sputtering Al target in methane atmosphere. The effects of Al content on the composition, microstructure and mechanical properties of deposited films were investigated. The tribological properties of deposited films were investigated in air and water. The results indicate that the sp²-C in the films increased, while the sp³-C in the films was restrained with the increasing metal content. With the increase of the sp²-C, the tribological properties of the films in water were improved because of the enhanced surface graphitization. Meanwhile, the content of Al of the films was adjusted by varying R.F power. Because of the appropriate Al content, the films exhibited excellent tribological performance both in water and air.