The friction and wear properties of MoS2 micro-sized spheres (MS-MoS2) modified by Cyanex 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) as additive in liquid paraffin (LP) were studied and compared with those of commercial colloidal MoS2 (CC-MoS2) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. The worn surfaces were examined with SEM and XPS, respectively. The results showed that the Cyanex 302-modified MS-MoS2 was a better extreme-pressure and antiwear and friction-reducing additive in LP than CC-MoS2. The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the alkyl and active elements (S, O, and P) in Cyanex 302 and tribochemical reaction and deposition film containing MoS2, Fe2O3, and FePO4. Moreover, the coexistence of sliding and rolling frictions in the lubricant of MS-MoS2/LP also contributed to the enhanced tribological properties.