Abstract: The changes of chemical components and tribological properties of TiN MoS x /Ti composite coatings caused by largely ion etching S from its surface are studied by XPS. After long time ion etching, the surface Mo/S ratio of the composite coatings decreases from 2 03 to 1 25 with a concomitant reduction in the Mo 3d 5/2 binding energy from 231 73 eV to 231 07 eV. After 5 minutes ion etching, the surface of coatings presents a deep black colored compact structure with excellent tribological properties; but after 15 minutes ion etching, the surface of the coating presents a french grey colored loose structure with greatly decreased tribological properties.