The electrophoretic mobility is measured by a photocorrelation spectroscopic method to derive zeta-potential as a function of pH using gold nanoparticles with a well-defined surface. Since the Debye length, 1/kappa, of the dispersion ranges from 0.5 to 340 nm and the radius of a particle a is in nanometer scale, we use a recently developed formula (Ohshima, H. J. Colloid Interface Sci. 2001, 239, 587) for the estimate of zeta-potentials which is applicable to wide kappaa region. The zeta-potentials derived are compared with those of theoretical ones in which we use only molecular parameters such as dissociation constants of mercaptosuccinic acid and given parameters such as a particle size, pH, composition of electrolyte in a dispersion, that means no adjustable parameters used. Qualitative agreement was attained between zeta-potentials and surface potentials purely from theory.