Abstract: N-doped TiO₂ thin films were prepared by sol-gel method with ammonium nitrate as N source.The products were characterized by UV-VIS，SEM，FTIR，and XRD.The influences of N-doping on photocatalytic property of titanium dioxide were discussed with the methylene blue as the degradation model.Results indicated that the redshift of the absorption band could be found obviously，and the photocatalytic activitiy was the best，when the N-doping dosage was 11% and the calcination temperature of thin films was 450 ℃.With the increased amount of N doping，the photocatalytic activitiy of thin films increased firstly，and then decreased.The main reason was that the growth of crystalline phase，BET surface and flaw could be all affected effect after N-doping.As for the change of photocatalytic activitiy，because the crystal transition and crystallinity were affected by calcination temperature，the effect of calcination temperature was the same as the amount of N-doping.

Key words: N-doping, TiO₂, photocatalysis