PURPOSE: To separate rare earth elements in high purity and high recovery rate even in the case where a polystyrene strongly acidic ion exchange membrane is used by using heavy metal ions as a resin accepting agent and also using, as a chromatography developer, a complexing agent containing specific salts.

CONSTITUTION: In the separation of rare earth elements by an ion exchange chromatography method, a polystyrene strongly acidic ion exchange resin is used as cation exchange resin. As a resin accepting agent, about 5-15g/l heavy metal ions are used. As a chromatography developer, a complexing agent containing salts selected from ammonium salt, potassium salt, and sodium salt by 10-400millimol/l is used. As a solution containing rare earth element ions to be the object, e.g. a liquid (containing Sm, Gd, Pr, Nd, Tb, Dy, etc.) separated by a solvent extraction method and then stripped out with hydrochloric acid is cited. By this method, the length of time necessary to separate rare earth elements can be shortened.