A method for producing an alkyl (3R,5S)-7-[2-cyclopropyl-4-(4-fluorophenyl)quinolin-3-yl]-3,5-dihydroxy-6- -heptenoate of the formula (1) (wherein R is a C.sub.1-4 alkyl group), which is an intermediate for a cholesterol-reducing agent (a HMG-CoA reductase inhibitor), etc. A solution containing a compound of the formula (1) is subjected to liquid chromatography treatment using silica gel as the packing material, to separate its epimers contained therein. ##STR00001##
