MoS2/a‐C:H multilayer film and MoS2/a‐C:H composite film exhibit excellent tribological properties in vacuum, which can be used as the potential space lubricant. The radiation‐protective properties of these two films in atomic oxygen (AO) are evaluated. The influences of AO radiation on structure, morphology, and tribological properties of the films were investigated. The results show that AO radiation mainly causes oxidation and increases sp2 C content in both of the films. Furthermore, the MoS2 sublayer on the surface of the multilayer film is oxidized heavily, whereas both the MoS2 and the a‐C:H matrix on the surface were oxidized in the composite film. As a result of this, the multilayer film exhibits high friction coefficient and short sliding lifetime in vacuum after AO radiation. Compared with that, the composite film exhibits lower friction and longer sliding time more than 3600 seconds in vacuum, which illustrates it has a good AO radiation protection. This indicates that MoS2/a‐C:H composite film is more likely to be used as a potential space lubricant.