The effect of gamma radiation on the electrical conductivity of polyaniline in the reduced, undoped and doped states has been studied. A model based on the oxidation of the polymeric chain combined with radiolysis of the adsorbed water molecule has been proposed to explain the radiation-induced effects in this polymer. The experimental results show that the film resistance of emeraldine base, and leucoemeraldine salts decrease drastically with exponential decay for the range from 0 to 250 Gy, when exposed to gamma radiation, while for emeraldine salt the resistance slightly decreases with exponential decay for low doses of radiation and increases linearly for high doses. Infrared analysis performed in irradiated emeraldine base strongly support a proton doping effect of the polymeric material induced by radiation.