The present invention provides a separating agent for enantiomeric isomers exhibiting high separation power. That is, the present invention provides a separating agent for enantiomeric isomers including, as an active ingredient, a polysaccharide derivative having at least part of hydrogen atoms of hydroxyl groups of a polysaccharide such as cellulose or amylose substituted by at least one of atomic groups represented by the following general formulae (I) and (II): (in the formulae, R represents a substituted or unsubstituted aromatic group, or a linear, branched, or cyclic aliphatic group).