Electrochemical and thermal measurements were carried out simultaneously on polyaniline in 1M ZnSO4 aqueous solution. An exothermic change at lower potential and an endothermic change at higher potential were observed on the surface of the polyaniline electrode during the anodic oxidation. The proportional relation between integral Delta Tdt and electric quantity was recognized in the thermal response to anodic constant current. The thermal response obtained here may be mainly attributed to the entropy change for two electrochemical processes of doping of SO42- ions and proton elimination. Temperature-dependence of electrode potential of the polyaniline oxidized anodically in ZnSO4 aqueous solution was examined to evaluate the entropy change for electrochemical dedoping process of SO42- ions.