The tribological properties of nano-MoS2 as additive in lubricating oils were studied. The nano-MoS2 based lubricating oil was prepared by dispersing nano-MoS2 in the base oil with different surface modifier and at different ultrasonic dispersion time, and the effect on dispersion stability of nano-MoS2 by the different surface modifier and different ultrasonic dispersion time was investigated. The tribological properties of nano-MoS2 based lubricating oil were studied by Four-Ball Test Machine and SEM. The results show that nano-MoS2 has good dispersion stability in the base oil when with 2% oleic acid as surface modifier and at the ultrasonic dispersion time of 30 min. Nano-MoS2 as additive in lubricating oils has good property of anti-wear and friction reducing properties, especially for 0.01% nano-MoS2 based lubricating oil, which is best in anti wear and friction reducing property under high load.