The positron lifetime spectra and electrical conductivities have been measured for polyaniline as a function of protonation level ([H⁺] from 10^-7—10^0.8 mol/L). We observed that (1) the short lifetime τ₁, which was related to electron density in bulk, decreased with the protonation level; (2) the intermediate lifetime τ₂≈360ps, almost remaining constant, whereas its intensity I₂ increased with increasing protonation level which was related to the conductivity of material. These results are discussed in terms of conducting island model.