PURPOSE: To perform inexpensively and efficiently adsorptive separation of an aimed isomer from a mixture of isomers.

CONSTITUTION: A clay intercalation compd. is used as an adsorbent and after an aimed substance is adsorbed thereon by bringing it into contact with a mixture of isomers, the aimed substance is separated by eliminating it therefrom. In another way, unnecessary substances are adsorbed to obtain the aimed substance from the mixture. It is possible thereby to perform easily and efficiently separation of isomers each other which can be hardly done by means of the conventional techniques as the clay intercalation compd. gives a large fine pore diameter and the fine pore diameter can continuously be controlled. It is also possible to easily control selectivity of adsorption and to cope with various purposes for separation.