Focussing chromatography was applied to the mutual separation of rare earth elements and the effect of several conditions upon the separation of rare earth elements was studied. The most satisfactory result was obtained in the conditions as follows: 0.1 M citric acid was used as the complexing agent and 0.01 N hydrochloric acid as the decomplexing agent, pH gradient of both solutions between anode and cathode was pH 2.8 (HCl)-4.4 (citric acid), the rare earth solutions contained no nitric acid, the applied voltage was 1, 000V/30 cm, the treatment time was 20 min, and the filter paper was Toyo Roshi No. 50.After treatment of separation, the autoradiographic technique was employed to decide the position of each separated line.