Polypyrrole doped by p-tolyl sulfonic acid was chemically synthesized from pyrrole using p- tolyl sulfonic acid as a doping agent and ferric chloride as an oxidant. The effect of dosage of the doping agent and the oxidant on the conductivity of doped polypyrrole was investigated, and the optimized conditions were obtained. The molecular structure of the polypyrrole was characterized by UV and IR spectra, and its morphology was studied by SEM. The results indicated that the polypyrrole was regular, and its conductivity reached 42.7 S•cm^－1, when the ratio of n(p-tolyl sulfonic acid)∶n(pyrrole)∶n(ferric chloride)＝0.75∶1∶0.5. A film containing the polypyrrole was prepared on magnesium surface, and its anticorrosion property was investigated by potentiodynamic polarization curves and open circuit potential. It was found that the polypyrrole showed an excellent anticorrosion property for magnesium, the corrosion current and voltage were measured to be 0.0981 A and －0.88 V, respectively, and a passivation layer was formed between the film and magnesium surface.

Key words: p-tolyl sulfonic acid, polypyrrole, doping, conductivity, anticorrosion