Oxalic acid is photooxidized on Sm2O3 and the oxidation follows first-order kinetics with a linear dependence on light intensity. The photocatalytic efficiency is higher with UV-C light than with UV-A light. While TiO2, ZnO, CuO, Bi2O3 and Nb2O5 individually photocatalyze the oxidation each semiconductor exhibits synergistic effect when present along with Sm2O3 indicating interparticle electron-jump from oxalic acid adsorbed Sm2O3 to the band gap-excited semiconductor on collision. The ease of photooxidation of the acids on Sm2O3 is: formic > oxalic > acetic > citric.