Abstract: The in-situ absorbance-time curves at λ=950 nm were measured during triangular potential scan of PPy(Cl) film. A cyclic voltammogram can be obtained from the time derivative of the absorbance. The effects of capacitance current and H~+ discharge in aqueous solution could be elimenated completely in the cyclic voltammogram obtained in this way. Selection of light wavelength and the limitation of the method are discussed.