Electrochemical quartz crystal microbalance (EQCM) was used to study the redox reaction of polypyrrole (PPy) prepared in an aqueous solution containing anionic surfactant. EQCM result confirmed that the small cation in the electrolyte solution rapidly moved into/out of the PPy film during redox reaction at a potentiodynamic condition and also the bulky anion, dodecylsulfate ion (DS-), additionally took part in redox reaction, especially in positive potential range above -0.2 V. The movement of anion was more clearly seen at potentiostatic condition than in voltammetric measurement, which implies the rate dependency of the anion movement in PPy film.