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The preparation method of a self-supporting doped-polyaniline film electrode and its open-circuit potential (OCP) in NaClO4 and Na2SO4 solutions with different pH value as well as cathodic polarization behavior have been investigated for the purpose of discussing the corrosion electrochemical behavior of polyaniline (PANI) in the acid solution. X-ray photoelectron spectroscopy (XPS) reveals that the lower pH corresponds to higher doping level of H+ in the film and a more positive OCP of PANI film electrode. OCP of the PANI film reached 0.35 V vs. SCE in 1M H2SO4, which is more positive than that of most metals, suggests that PANI would act as cathode when it couples with these metals. The cathodic polarization experiments indicate that the dominating cathodic polarization process of PANI is reversible doping and dedoping reaction and the reduction of dissolve oxygen has very little contribution to it. The potentiostatic current-time curves exhibit a large transient current density at initial stage of polarization, which should be attributed to the charge stored in the film and a relative less steady state current density at the subsequent stage of polarization, which is provided by its doping/dedoping equilibrium activity. Such a current characteristic of PANI electrode might be the force of PANI to provide the passivation protection for some active-passive metals.