Fe~ 3+ -doped nanometer TiO_2 photocatalysts were prepared by sol-gel technique. TiO_2 powders with different Fe~ 3+ /Ti~ 4+ molar ratios ranging from 0.05% to 25% were synthesized by calcinating the gels in the temperature range of 200-600 ℃. The effects of the content of iron ions and calcination temperature on the physical properties of the powders and their photocatalytic activities were examined by the photodecompositon of methyl orange in sunlight. The results show that Fe dopant can decrease the temperature of nanatase-rutile transformation. The ideal photocatalytic property was achieved when the sample with an Fe~ 3+ /Ti~ 4+ ratio of 20 at% was calcined at about 300 ℃ for an hour, which is superior to that of commercial Degussa P-25. The optimum microstructure of the Fe-doped TiO_2 for a high photocatalytic activity in sunlight is consisted of nanatase and rutile. Fe ~ 3+ -doped nanometer TiO_2 photocatalysts were prepared by sol-gel technique. TiO_2 powders with different Fe ~ 3+ / Ti ~ 4+ molar ratios ranging from 0.05% to 25% were synthesized by calcinating the gels in the temperature range of 200-600 ° C. The effects of the content of iron ions and calcination temperature on the physical properties of the powders and their photocatalytic activities were examined by the photodecompositon of methyl orange in sunlight. The results show that Fe dopant can decrease the temperature of nanatase -rutile transformation. The ideal photocatalytic property was achieved when the sample with an Fe ~ 3+ / Ti ~ 4+ ratio of 20 at% was calcined at about 300 ° C for an hour, which is superior to that of commercial Degussa P-25 . The optimum microstructure of the Fe-doped TiO 2 for a high photocatalytic activity in sunlight is consisted of nanatase and rutile.