Hydrogenated amorphous carbon (a-C:H) films have been applied in many mechanical components because of their prominent mechanical and tribological properties. Since these properties of a-C:H films are deeply correlated with their microstructure, it is important to understand the microstructure of a-C:H films and then discuss the friction properties of a-C:H films in a microstructural point of view, to clarify the friction mechanism. In this study, the microstructure of a-C:H films was analyzed by Raman spectroscopy, and the friction tests were conducted using pin-on-disc type tribotester in the air. It was found that the frictional properties of a-C:H films depend on their microstructure, i.e., polymer-like carbon (PLC), diamond-like carbon (DLC) and graphite-like carbon (GLC) structures. The PLC and GLC-structured a-C:H films show lower friction coefficients compared to that of the DLC-structured film. Two different trends are observed in the relationship between the hardness and the friction coefficient with respect to the microstructure of a-C:H films. The chemistry of the friction interface is dependent on the microstructure of a-C:H films, which affects to the friction coefficient.