Poly(2,2′-dithiodianiline) [poly(DTDA)], which is a conducting polymer interconnected with disulfide (SS) bonds, was studied electrochemically in acidic aqueous media. Redox reactions and structural changes of the poly(DTDA) in acidic aqueous solutions at various applied potentials and pH values were investigated. A Pourbaix diagram [potential (E)–pH profile] for the poly(DTDA) was plotted in order to distinguish the structures of the poly(DTDA) for the applied potentials and the pH values. The detailed structural changes were characterized using in situ UV–vis and surface-enhanced Raman spectroscopies.