Abstract: The TiO₂ nanoparticles doped by Mo⁶⁺, Cr³⁺ and Fe³⁺ ions with the ion concentration of 0.05%（mol） were prepared by the Sol-Gel method at calcination temperatures of 550℃ and 580℃, and characterized by XRD, BET and FT-IR.The results showed that Mo⁶⁺ ion doping efficiently inhibited the phase transformation of TiO₂ at different temperatures, while Cr³⁺ and Fe³⁺ ion doping played a reverse effect at 550℃ and 580℃ respectively, which might be caused by the disparate status of doping ion in the titania crystals due to different calcination temperatures.The photocatalytic decomposition of dye rhodamine B was utilized to evaluate the influences of calcination temperature and ion concentration on the photocatalytic activities of doped nano-sized TiO₂.It was found that the influences of ion doping on the photocatalytic activities of titania were consistent with the influences of ion doping on phase transformation.The TiO₂ doped by Mo⁶⁺ with the ion concentration of 0.05%（mol） showed the highest photocatalytic activities.