The preparation and the photocatalytic degradation NO2 - activity of Fe3+-doped TiO2 nano-sized particles is reported in this paper. The TiO2 nano particles were prepared by sol-gel method. The various influence factors about the synthesis process of the Fe3+-doped TiO2 nano photocatalyst were controlled and investigated by XRD (X-ray diffraction), SEM (scanning electron microscopy), and TEM (transmission electron microscopy) etc.. The results show that the phase compositions, crystalline grain size, crystal structure , and photocatalytic activity of the Fe3+-doped TiO2 particles prepared by the method depend on the synthesis technology parameters such as calcination temperature, holding time, Fe3+ ions concentration etc.. The influence factors of the preparation process has been discussed. The photocatalytic decomposition of NO2 - ion into N2 and O2 using Fe3+ and Ce4+-doped TiO2 photocatalysts were investigated under UV irradiation. It was fund that Fe3+-doped TiO2 photocatalysts shows much higher photocatalytic activity than that of the Ce4+-doped TiO2 . The photocatalytic decomposition effect of NO2 - ion is related to the crystalline grain size, irradiation time, and the Fe3+ ions concentration. The Fe3+-doped TiO2 nano powders exhibited the photocatalytic degradation NO2 - activity under UV light irradiation.