Poly(ethylene terephthalate) (PET) was incorporated with different amounts of TiO2 nanoparticle and then spun into fibers of different diameters. Surface properties of these modified fibers were investigated by friction force, scanning electron microscopy, energy dispersive X-ray analysis, and electron spectroscopy for chemical analysis (ESCA). TiO2 nanoparticles showed aggregation on the fiber surface. The number of aggregates increased as the amount of TiO2 nanoparticle increased and/or the diameter of spun fiber decreased. These were evidenced from SEM and also from an increased C(1s)/O(1s) ratio in the ESCA spectra. The aggregates of TiO2 nanoparticle on the fiber surface cause unevenness, leading to a decreased friction-contact area between surface of the sliding fiber and its encountered surface. Thus, the friction force that arose from the interface reduced. In addition, on the basis of different amounts of TiO2, a broad range of fiber frictions could be formed. This would provide promise to potential performance in fiber industry.