Eight lanthanide oxides were used sep. as a catalyst in the electrolysis of O-2 on Pt electrode at 298 and 328 K to det. the reaction kinetics by chronopotentiometry. The highest catalytic activity was obsd. for Pr2O3 and Sm2O3 at 298 K. It decreased with temp. rise achieving values close to Tr2O3 activity at 328 K.