The effects of counterions on surfactin-C(16) micelle solution with its critical micelle concentration (cmc), microenvironment properties in micelles, micelle size distribution, and morphology were investigated by fluorescence, dynamic light-scattering, and freeze-fracture transmission electron microscopy measurements. Counterions enhanced the surface activity of surfactin-C(16) and reduced the cmc. With the micellization of surfactin-C(16), it adopted a beta-sheet conformation, and univalent concentrations reduced micelle micropolarity, increased micelle microviscosity, and tended to cause formation of small and spherical micelles, while divalent counterions had a special effect. With low concentration of divalent cations, they had strong interaction with surfactin-C(16) micelles and tended to form larger micelle aggregates.