Novel prostaglandin derivatives represented by general formula (I), pharmaceutically acceptable salts thereof, or hydrates of both, wherein X is CH2, O, S, or the like; Y is ethylene, vinylene, ethynylene, or the like; Z is ethylene, vinylene, or ethynylene; R is hydrogen, alkyl, or cycloalkyl; R is alkyl, alkenyl, alkynyl, cycloalkyl, or the like; and R is hydrogen, alkyl, or the like. The prostaglandin derivatives exhibit an excellent inhibitory activity against the proliferation of vascular smooth muscle and are useful as preventive or therapeutic drugs for post-PTCA restenosis and so on.