PROBLEM TO BE SOLVED: To provide novel cosmetics for moisturizing effect.SOLUTION: A 4-alkyloxazolidin-2-one represented by the specified formula is used as a moisturizing cosmetic agent for producing a moisturizing cosmetic composition. [R is a linear or branched alkyl group comprising 4 to 24 carbon atoms, preferably 4 to 18 carbon atoms, or a linear or branched alkylene group comprising 4 to 24 carbon atoms, preferably 4 to 18 carbon atoms.]【課題】保湿効果のための新規な化粧品の提供。【解決手段】下記式で表される4-アルキルオキサゾリジン-2-オンの、保湿化粧品組成物の製造用の保湿化粧剤としての使用。[Rは4個~24個のC、好ましくは4個~18個のCを含む直鎖若しくは分岐鎖アルキル基、又は4個~24個のC、好ましくは4個~18個の炭素原子を含む直鎖若しくは分岐鎖アルキレン基]【選択図】なし