The conducting polymer poly(5-hydroxy-1,4-naphthoquinone-co-5-hydroxy-3-acetic acid-1,4- naphthoquinone) with electroactive quinone group was investigated by Electrochemical Impedance Spectroscopy (EIS) in aqueous medium. The evaluations of parameters of equivalent circuit in term of applied potential were considered. The simulated EIS data presented a good agreement with the results obtained by other electrochemical methods.