Lanthanide doped ZnO nanoparticles with different Ln (Ln = La, Nd and Sm) contents were synthesized by polymer pyrolysis method and characterized by various techniques such as XRD, UV-vis, SEM, TGA, and TEM. The XRD results revealed that Ln(3+) is uniformly dispersed on ZnO nanoparticles in the form of small Ln(2)O(3) cluster. From SEM and TEM images it was found that the particle size of La-doped ZnO is much smaller as compared to that of pure ZnO. The photocatalytic activity of La-doped ZnO in the degradation of 4-nitrophenol (4-NP) was studied. The effects of the type and amount of loadings on the photocatalytic activity of Ln-doped ZnO were studied and the results were compared with pure ZnO. It was observed that the rate of degradation of 4-NP over Ln-doped ZnO increases with increasing La, Nd and Sm loading up to 4,4 and 8 wt% and then decreases. It was found that the doping of Ln in ZnO helps to achieve complete mineralization of 4-NP within a short irradiation time. Among the catalysts, the 4 wt% Nd-doped ZnO was the most active and showing high photocatalytic activity for the degradation of 4-NP. (C) 2012 Elsevier B.V. All rights reserved.