Ac-modulated UV-vis reflectance spectroscopy was applied to elucidate the electrode reaction rate bf the species immobilized on electrode surfaces. The electroreflectance (ER) with respect to the electrode potential at constant wavelength, denoted as ER voltammetry, was analyzed theoretically using numerical calculation. In the present calculation, the amplitude of the ac modulation, the IR drop due to the solution resistance, and the double layer capacitance were taken into account. The results of the calculation were compared to the electrode reaction of cytochrome c immobilized on an SH(CH2)(9)COOH self-assembled monolayer modified gold electrode, which has previously been studied. The standard rate constant of the electrode reaction of cytochrome c(3) adsorbed directly on gold electrode was determined to be 200 s(-1) using non-linear least square fitting to the experimental data. This approach is applicable to unstable redox species at the electrode surface, e.g. cytochrome c(3), which desorbs gradually from the gold electrode surface at negative electrode potential. That is, one can determine the kinetic parameters of adsorbed redox species by a single potential scan.