In this report. we demonstrate electrocatalytic oxidation properties of ascorbic acid at poly(3,4-ethylenedioxythiophene) (PEDOT) thin films in view of their potential application for big-sensing devices. PEDOT thin films were deposited on gold thin films by electropolymerization of EDOT monomer in acetonitrile solvent. In-situ electrochemical-surface plasmon resonance spectroscopy (EC-SPR) was used to detect both electrochemical and optical signals upon an injection of ascorbic acid.