A surface wave mode on a gel has been studied as a function of thickness by using electrically excited surface wave spectroscopy (EESWS), which measures the response of excited surface waves by applying an electric field at the surface. In the frequency region where the elastic and surface tension forces dominate, multiple harmonics of a surface mode are predicted theoretically for a finite-thickness case due to a coupling with the normal direction wave to the surface. This paper shows the rst experimental measurement of the multiple harmonics of a surface mode. We have compared the experimental data with the theoretical calculation.