As a kind of surface-active agent, toluene-p-sulfonic acid (p-TSA) could be used to pre-disperse La2O3. On the other hand, p-TSA was also a protonic acid. The electric conduction of polyaniline (PANI) could be obtained by doping with it. According to these properties, PANI/La2O3 nanocomposite was synthesized by a chemical method. The electrical conductivity was measured by a four probe method. The nanocomposite was characterized by SEM, EDS, XRD and FT-IR. The result indicated that the electrical conductivity of PANI and PANI/La2O3 were 1.0 •and 1.9 S•cm－1, the particle diameters were about 200 and 50 nm, respectively. The doping of La2O3 could reduce the diameter, and meanwhile did not lower the conductivity of PANI. The products were also characterized by cyclic voltammetry. The result showed that doping of La2O3 raised oxidative (and reductive) peak current densities and restrained the electrochemical degradation of PANI in aqueous solutions containing 0.25 to 2.00 mol•L－1 sulfuric acid or phosphoric acid•.