The objective of the present invention is to provide a method for remarkably reducing a critical micelle concentration of an anionic surfactant, which is used in a large amount currently, to reduce the amount to be used. Also, the objective of the present invention is to provide a surfactant composition of which whole critical micelle concentration is remarkably reduced and in which an amount of an anionic surfactant is reduced in comparison with the case of using an anionic surfactant only as a surfactant. The method for reducing a critical micelle concentration of an anionic surfactant according to the present invention is characterized in using a cyclic lipopeptide biosurfactant in combination with the anionic surfactant.
