Rutile TiO2 nanoparticles with new sites for effectively trapping photogenerated holes have been prepared by reacting the TiO2 nanoparticles prepared in hydrogen atmosphere with molecular oxygen at elevated temperatures. The observed g values and the occurrence of Ti-47 and Ti-49 octet hyperfine pattern allowed us to assign this ERR active center to surface oxygen centered anion radical with two coordinating titaniums. The effective trapping of photogenerated holes by these new sites inhibits the electron hole recombination and results in an enhanced photocatalytic activity under visible light by a factor of 2.5 compared with samples prepared parallel in air. Oxidation of reduced TiO2 apparently is a simple low-cost and promising route for improving the photoactivity of TiO2.