Impedance studies of a copper electrode in a chloride medium with or without benzotriazole (BTA) were made over a wide frequency range (10Hz - 100kHz). The results indicated that the film was of a dielectric nature having a dielectric constant of ca. 20. The film thickness increased and the corrosion rate decreased by increasing the BTA-concentration or with aging. At the stationary state, the rate of dissolution of Cu-BTA film balanced that of the slow transport of Cu ions through the film. Good support for these results was obtained from the data of potentiostatic polarization and weight loss measurements. -- AATA