In order to investigate stability of spherical sodium dodecyl sulfate micelle in water, molecular dynamics calculations have been performed for the micelle of various sizes. Size-dependence of the micelle structure such as asphericity, Voronoi polyhedron, and radial density profile has been analyzed in detail from a viewpoint of geometrical instability found in it, i.e., direct exposition of the hydrophobic group to water observed for small micelles and cavity formation in the center of large micelles. (c) 2006 Elsevier B.V. All rights reserved.