Abstract: A 4-hydroxy-2-cyclopentenone represented by the following formula (I) ##STR1## wherein X represents a hydrogen or halogen atom, A represents a hydrogen atom and B represents a hydroxyl group, or A and B are bonded to each other to represent a bond, R.sup.1 represents a substituted or unsubstituted alkyl, alkenyl or alkynyl group having 1 to 10 carbon atoms, R.sup.2 represents a substituted or unsubstituted alkyl, alkenyl or alkynyl group having 1 to 10 carbon atoms, and R.sup.3 represents a hydrogen atom or a protective group for a hydroxyl group, provided that R.sup.2 is not a 2-octenyl, 8-acetoxy-2-octenyl or 2,5-octadienyl group. The compounds of formula (I) in which A is hydrogen and B is hydroxyl group are prepared by subjecting a 5-unsubstituted cyclopentenone and an aldehyde to aldol condensation reaction. The compounds of formula (I) in which A and B form a bond is prepared by subjecting the compounds of the formula (I) in which A is hydrogen and B is hydroxyl group to dehydration.