Abstract: The changes in the conductivity and electron spin resonance intensity of polyaniline before and after reduction with temperature have been reported. The energy band gap E_g of polyaniline after reduction is 0.252 eV which was obtained from the plot of logσ vs.1/T, its unpaired electron density is approximately 1.84×10~(23)m~(-3) or 1.06×10~(20)kg~(-1), its conductivity-temperature relation is given by σ_t= σ_(20)-9.17×10~(-4) (20-t) S.m~(-1). The conductivity of polyaniline before reduction decreases with rising temperature above 20 ℃ and increases with rising temperature below 20 ℃. Its unpaired electron density is approximately 2.55×10~(27)m~(-3) or 1.47×10~(24)kg~(-1). The density and peak-peak linewidth ΔH_(p-p) of the electron spin resonance of both forms of polyaniline change with temperature. Each of susceptibility of polyaniline before reduction is zero at the different temperatures.