The effect of grain boundary (GB) defects on the tribological properties of MoS₂ has been investigated by molecular dynamics (MD) simulations. The GB defects-containing MoS₂ during scratching process shows a lower critical breaking load than that of indentation process, owing to the combined effect of pushing and interlocking actions between the tip and MoS₂ atoms. The wear resistance of MoS₂ with GB defects is relevant to the misorientation angle due to the accumulation of long Mo-S bonds around the GBs. Weakening the adhesion strength between the MoS₂ and substrate is an efficient way to improve the wear resistance of MoS₂ with low-angle GBs.