Lanthana-doped mesoporous TiO2 nanoparticles with high specific surface area and thermal stable anatase wall was synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting materials were characterized by XRD, FESEM, TEM, FT-IR spectroscopy, and nitrogen adsorption. The as-synthesized mesoporous doped TiO2 nanoparticles have mean diameter of 20nm with mean pore size of 2.2nm. The specific surface area of the as-synthesized mesoporous nanosized doped TiO2 exceeded 460m2/g, and that of the samples after calcination at 500℃ still have 243m2/g. Compared with undoped sample and P25, the lanthana-doped mesoporous TiO2 nanoparticles show better activities on the oxidation of rhodamine B (RB). The large surface area and more active sites for combining with RB due to the present of lanthanum ion can explain the high photocatalytic activity of lanthana-doped mesoporous TiO2 nanoparticles.