Polyethylene (PE) nanoparticles were newly prepared by a combination of ultrasonication and low-temperature-induced crystallization in poly(ethylene glycol). These PE particles were formulated into spin finishes and applied to the surface of titania-modified poly(ethylene terephthalate) (PET) fibers that had a higher relative concentration of titania (TiO2) nanoparticles at the fiber surface than in the interior core as evidenced by SEM/EDX mapping studies. Aggregations Of TiO2 nanoparticles were found to appear oil the surface of such fibers, which led to a decreased contact area and, thus, an increased contact pressure between the sliding fiber and its encountered surface. The effect of plowing by the sliding fiber oil its counterpart was observed and studied as a function of the PE nanoparticle size, and the corresponding data oil the friction force among three values of fiber fineness were also obtained. We found that the fiber friction force decreased and the plowing effect oil its counterpart increased when the fiber fineness decreased. In addition, we found that the minimum plowing effect was obtained when the size of the PE nanoparticles was comparable to the size of the TiO2 aggregations that appeared on the surface of the titania-modified PET fibers.