The structural changes associated with the protonation of polyemeraldine base by various protonic acids were studied by X-ray photoelectron spectroscopy (XPS). The imine, amine and positively charged nitrogen corresponding to a particular oxidation state and protonation level were quantitatively differentiated in the properly deconvoluted N1s core-level spectrum. The actual degree of protonation in the HCl and HBr complexes was determined from the halogen anion core-level component. The anion in the H2SO4 complex was found to be the monovalent HSO4− species. Treatment of the HBr, HNO3, and H2SO4 protonated polyemeraldine with HCl readily resulted in the exchange of the anion species.