Comparison was made of the adsorption of iodide ion on gold electrode by the specular reflection method with that by the electrochemical quartz crystal microbalance (EQCM). Reflectivity was noted to decrease at potentials more positive than -0.8 V on the reflectivity change-potential curve of gold due to the presence of NaI in 0.1 M NaClO4. The oscillation frequency of quartz crystal covered with gold decreased at potentials more positive than -0.8 V as a result of iodide ion adsorption. The potential dependence of reflectivity change was essentially the same as that of frequency change determined by EQCM. Maximum frequency change due to adsorption at 1.0 x 10(-4) M NaI at -0.1 V corresponded to monolayer coverage, and thus it was possible to calculate surface coverage, theta, from a given frequency or reflectivity change. The Temkin parameter, r, and electrosorption valency, y, could be determined from the Temkin isotherm. The data obtained by both methods showed close agreement. The specular reflection method is thus reconfirmed as a method for analyzing anion adsorption data.