Lanthanide ions (La3+ Nd3+, Sm3+, Eu3+, Gd3+, and Yb3+)/doped TiO2 nanoparticles were successfully synthesized by sol-gel method. Their photocatalytic activities were evaluated using Direct Blue dye (DB53) as a decomposition objective. The structural features of TiO2. and lanthanide ions/TiO2 were investigated by XRD, SEM, UV-diffuse reflectance, and nitrogen adsorption measurements. Our findings indicated that XRD data characteristic anatase phase reflections and also XRD analysis showed that lanthanides phase was not observed on Lanthanide ions/TiO2. The results indicated that Gd3+/TiO2 has the lowest bandgap and particle size and also the highest surface area and pore volume (V-p) as well. Lanthanide ions can enhance the photocatalytic activity of TiO2 to some extent as compared with pure TiO2 and it was found that Gd3+/TiO2 is the most effective photocatalyst. The photocatalytic tests indicate that at the optimum conditions; illumination time 40 min, pH similar to 4, 0.3 g/L photocatalyst loading and 100 ppm DB53; the dye removal efficiency was 100%. Details of the synthesis procedure and results of the characterization studies of the produced lanthanide ions/TiO2 are presented in this paper. (C) 2008 Elsevier B.V. All rights reserved.