Lanthanide metal-ion-doped TiO2 nanoparticles were prepared with hydrothermal method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP) and fluorescence spectrum. The results showed that a small part of metal ions entered into the lattice of TiO2 and others adsorbed on the surface of TiO2. The photoelectrochemical and photocatalytic properties of these lanthanide metal-ion-doped TiO2 nanoparticles were investigated and the results showed that the photoresponse of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 electrodes were much larger and that of Sm3+-doped TiO2 electrode was a little larger than that of undoped TiO2 electrode, indicating that the photogenerated carriers were separated more efficiently in Eu3+, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles than in undoped TiO2 nanoparticles. The photocatalytic degradation of rhodamine B (RB) was conducted in the suspension of lanthanide metal-ion-doped TiO2 nanoparticles, and its first-order reaction rate constant (k) and average initial rate (r(ini)) were significantly higher in the presence of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles than those in the presence of undoped TiO2 nanoparticles. The enhanced photocatalytic degradation rate of RE in the presence of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles is attributed to increased charge separation in these systems. The effect of the content of La3+ on the reaction parameters (k and r(ini)) was also investigated and the result showed that there was an optimal value (ca. 0.5%) of the content of La3+ to make the rate constant (k) and average initial rate (r(ini)) reach the maxima.