Electron paramagnetic resonance (EPR) measurements are performed for F center in high-surface-area anatase titania nanoparticles prepared by MOCVD. It is found that with increasing temperature, there is a critical temperature range from 353 to 413 K, in which the linewidth (peak to peak) of the EPR signal increases from 4.20 to 4.98 G. Below 353 K, the linewidth is 4.20 G, while above 413 K the linewidth is kept constant at 4.98 G. The temperature dependence of linewidth is obviously different from the commonly hold view that temperature affects the intensity but does not affect the linewidth of EPR signal of F center in oxides. The adsorbed water on the surface of the nanoparticles is responsible for the line broadening. (C) 2004 Elsevier B.V. All rights reserved.