Nano-TiO2 and Fe3 ,Ce3 doped TiO2 particles in different sizes have been prepared by sol-gel method.XRD and TEM analysis results show that the particle size of doped TiO2 decreased;TiO2 crystal phase transition could be prevented by doping Fe3 and Ce3 .The results of photocatalytic degradation of NO2-show that of all the degradations of nitrite by photocatalyst synthesized under the same condition of preparation and doping amount,the highest is that of Fe3 doped TiO2,the second is that of Ce3 doped TiO2,and the last is that of TiO2.