Nonequilibrium molecular dynamics (NEMD) simulations were performed to investigate the tribology behaviors of Al 2 O 3 and MoS 2 nanoparticles confined between iron (Fe) slabs. Results indicated that the combined use of these two nanoparticles yielded the lowest and most stable friction force, normal force, interface temperature and wear rate, which exhibited a significant synergistic lubrication effect. A novel parameter the rolling/sliding motion coefficient (K rs ) was proposed to evaluate the motion pattern of spherical Al 2 O 3 . There were 51% rolling ? 49% sliding motion when used alone and 91% rolling ? 9% sliding in the existence of MoS 2 . Similarly, about 72.3% of the friction was shared by interlayer sliding of MoS 2 monolayers in the presence of Al 2 O 3 , which was higher than used alone (54.8%). Then, the diffusion of atoms at the friction interface was explored to reveal the synergistic lubrication mechanism. The tribofilm formed by the diffusion of Fe and S atoms could protect the metal surfaces from further wear. The adsorption of S atoms to Al 2 O 3 nanoparticle could promote its rolling effect and prevent it from embedding into iron matrix. Besides, Al 2 O 3 could also facilitate the separation of MoS 2 monolayers to enhance their interlayer sliding effect.