Poly(ethylene plathalate) (PET)/nano-TiO2 composites prepared via in situ polymerization were spun into fiber by the melt-spinning process. The dispersion of nanosized rutile TiO2 in the PET was studied using transmission electron microscopy (TEM) and scanning probe microscopy (SPM) techniques. The mechanical properties and the properties of ultraviolet (UV) protection were investigated. The results showed that rutile TiO2 can be dispersed uniformly by the in situ polycondensation process. The mechanical properties of PET/TiO2 fiber were slightly affected by adding nano-TiO, The UV-ray transmittance of PET/nano-TiO2 fabrics was below 10% in the UV-A band and below 1% in the UV-B band. And the ultraviolet protection factor (UPF) of PET/nano-TiO2 fabrics was greater than 50. All these PET/TiO2 nanocomposite fabrics exhibited excellent UV-blocking properties. (c) 2006 Wiley Periodicals, Inc.