This study focuses on the possibility of improving performance properties of polydicyclopentadiene (PDCPD) nanocomposites for engineering applications using nanoparticles. In this article, molybdenum disulfide/polydicyclopentadiene (MoS2/PDCPD) nanocomposites have been prepared by in situ ring-opening metathesis polymerization using reaction injecting molding (RIM) process. To enhance the interfacial adhesion between the fillers and PDCPD matrix, the surface modified MoS2 nanoparticles hybridized with dialkyldithiophosphate (PyDDP) were successfully prepared by in situ surface grafting method. The effect of low MoS2 loadings (<3 wt %) on the mechanical and tribological behaviors of PDCPD was evaluated. The results indicated that the friction coefficient of the MoS2/PDCPD nanocomposites was obviously decreased and the wear resistance of nanocomposites was greatly improved by the addition of PyDDP-hybridized MoS2 nanoparticles; meanwhile, the mechanical properties were also enhanced. The MoS2/PDCPD nanocomposites filled with 1 wt % PyDDP-hybridized MoS2 exhibited the best mechanical and anti-wear properties. The friction coefficient was shown to decrease by more than 40% compared to pure PDCPD by incorporating just 1 wt % hybridized MoS2 nanoparticles, and modest increase in modulus and strength was also observed. The reinforcing and wear-resistant mechanisms of MoS2/PDCPD nanocomposites were investigated and discussed by scanning electron microscopy. The well interfacial compatibility between the particle/matrix interfaces played an important role for the improved mechanical and tribological properties of MoS2/PDCPD nanocomposites in very low MoS2 loadings. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013