Separation of a chemical substance is effected by treating a mixture thereof with a polysaccharide having a substituent for hydroxyl group an acyl group of the formula (1) or a carbamoyl group of the formula (2): ##STR1## wherein R represents an atomic group having a nucleus comprising a conjugated .pi.-bond system in which the number of bonds interposed between an atom contained therein and bonded with the carbonyl or amino group and an atom contained in the .pi.-bond system and most distant from said atom is at least 5 even in the shortest route.