A spectroelectrochemical study on the redox chemistry of polyaniline (PANI) was carried out by using indium-tin oxide (ITO) transparent electrode in aqueous acidic solutions. Three different PANI-derived species were observed depending on the potential. The most highly oxidized species having alternating benzenoid-quinoid structures degraded through hydrolysis reaction. The degradation products were confirmed to be p-benzoquinone (BQ) and p-diaminobenzene (PDAB) by spectrophotometry anld potentiostatic experiments. Finally, a degradation mechanism is deduced from the observed behaviour.