A method for preparing a prostaglandin derivative of formula: wherein A 1 is a hydrogen or a protecting group for a hydroxy group; Y is -OA 2, wherein A 2 is a hydrogen or a protecting group of a hydroxy group; W is -R 1 -Q, wherein R 1 is a saturated or unsaturated bivalent lower or medium aliphatic hydrocarbon residue, which is unsubstituted or substituted with halogen, lower alkyl, hydroxy, oxo, aryl or heterocyclic, and at least one of carbon atoms in the aliphatic hydrocarbon is optionally substituted by oxygen, nitrogen or sulfur, Q is -CH 3, -COCH 3, -OH, -COOH or a functional derivative thereof; or Y and W may both together form a group represented by the formula: wherein R 1 ' is a bivalent saturated or unsaturated lower to medium aliphatic hydrocarbon residue; R 3 is a saturated or unsaturated lower to medium aliphatic hydrocarbon residue that is unsubstituted or substituted with a lower alkoxy, a lower alkanoyloxy, a cyclo(lower)alkyl, a cyclo(lower)alkyloxy, an aryl, an aryloxy, a heterocyclic or a heterocyclicoxy; a cyclo(lower)alkyl group; a cyclo(lower)alkyloxy group; an aryl group; an aryloxy group; a heterocyclic group; a heterocyclicoxy group; X 1 and X 2 are a hydrogen, a lower alkyl group or a halogen; and Z is =CH- or -CH=CH-, provided that -OA 1 and Q may together form which comprises reacting an aldehyde represented by formula: wherein Y, W and A 1 have the same meanings as above; B is a single bond or -CH 2 -, with a 2-oxoalkyl phosphonate represented by formula: wherein X 1, X 2 and R 3 have the same meanings as above; and R 2 is a lower alkyl group; in a reaction solvent under the presence of alkali hydroxide as sole base and wherein no zinc compound is used. wherein A 1 is a hydrogen or a protecting group for a hydroxy group; Y is -OA 2, wherein A 2 is a hydrogen or a protecting group of a hydroxy group; W is -R 1 -Q, wherein R 1 is a saturated or unsaturated bivalent lower or medium aliphatic hydrocarbon residue, which is unsubstituted or substituted with halogen, lower alkyl, hydroxy, oxo, aryl or heterocyclic, and at least one of carbon atoms in the aliphatic hydrocarbon is optionally substituted by oxygen, nitrogen or sulfur, Q is -CH 3, -COCH 3, -OH, -COOH or a functional derivative thereof; or Y and W may both together form a group represented by the formula: wherein R 1 ' is a bivalent saturated or unsaturated lower to medium aliphatic hydrocarbon residue; R 3 is a saturated or unsaturated lower to medium aliphatic hydrocarbon residue that is unsubstituted or substituted with a lower alkoxy, a lower alkanoyloxy, a cyclo(lower)alkyl, a cyclo(lower)alkyloxy, an aryl, an aryloxy, a heterocyclic or a heterocyclicoxy; a cyclo(lower)alkyl group; a cyclo(lower)alkyloxy group; an aryl group; an aryloxy group; a heterocyclic group; a heterocyclicoxy group; X 1 and X 2 are a hydrogen, a lower alkyl group or a halogen; and Z is =CH- or -CH=CH-, provided that -OA 1 and Q may together form which comprises reacting an aldehyde represented by formula: wherein Y, W and A 1 have the same meanings as above; B is a single bond or -CH 2 -, with a 2-oxoalkyl phosphonate represented by formula: wherein X 1, X 2 and R 3 have the same meanings as above; and R 2 is a lower alkyl group;