The objective of this invention is to provide a process for producing an optically active isomer of ethyl 7-[2-cyclopropyl-4-(4-fluorophenyl)quinolin-3-yl]-3,5-dihydroxy-6-heptenoate by optically resolving an optical isomer mixture of the compound at a high productivity. The process is characterized by employing a filler comprising a carrier and a specific amount of cellulose tris (4-chlorophenyl carbamate) supported the carrier and carrying out chromatographic separation under the condition that the capacity factors have specific values.