In order to investigate shape of the micelles and its thermal fluctuations, molecular dynamics calculations have been performed for spherical ionic sodium dodecyl sulfate (SDS) and nonionic octaethyleneglycol monododecyl ether (C12E8) micelles. New statistical functions suitable for extracting the fluctuations of the shape of the spherical micelles were defined using spherical harmonics and Legendre polynomials. The breathing and deforming modes of the SDS and C12E8micelles were analyzed in detail based on these new functions. The elastic nature of the micelle core was also discussed. The present analysis gives a new molecular picture that the micelle shape is a superposition of the various kinds of breathing and deforming modes, and each mode has a specific relaxation time of the shape fluctuation.