An optically active dihydroxyheptenoic acid ester having an aromatic group is separated from a solution containing a mixture of optical isomers of digydroxyheptenoic acid ester by liquid chromatography with a packing material constituted of a carrier and a polysaccharide derivative carried on the carrier. The polysaccharide derivative is a polysaccharide in which the hydrogen atoms constituting the hydroxyl and amino groups are partially or all replaced by one or more kinds of groups selected from among carbamoyl groups monosubstituted with aromatic groups having specific alkyl groups and benzoyl groups having specific alkyl groups. According to the invention, optically active dihydroxyheptenoic acid esters can be separated more distinctly.