ESR spectra of polyaniline which had been synthesized electrochemically under various potentials and pH''s were studied. A reaction scheme has been proposed for the stepwise electrochemical oxidation of polyaniline. Upon oxidation of polyaniline, radical cations, i. e. the polarons are formed in the first step. Upon further oxidation, the radical cations gradually disappear and the quinoid structures are formed at the expense of the benzoid structures. Considering that the electrical conductivity of Polyanilline varies with the oxidizing potential almost in the same fashion as the relative ESR intensity, it is concluded that the ESR data obtained in this experiment are supportive of the radical cation mechanism for the electrical conductivity of polyaniline.