In this paper, the antiwear and antifriction performance of MoS 2 nanoparticle in castor oil was studied. The ball-on-disc tests were performed for different concentrations of MoS 2 nanoparticle. Coefficient of friction, wear loss, and worn surface morphology were investigated. The results show that MoS 2 nanoparticle could reduce the possibility of asperities direct contact, resulting in the reduction of the coefficient of friction and adhesive wear. However, MoS 2 nanoparticle in excessive concentration could agglomerate into large particles, playing the role of an abrasive particle, which reduces the beneficial effects of MoS 2 nanoparticle.