Electropolymerization of aniline in perchloric acid solutions was investigated with presence of para-phenylenediamine (PPDA). Experimental results showed that the presence of PPDA promoted markedly the growth of the polymer. The catalytic effect of PPDA on the polymerization of aniline included its contributions to both the autocatalysis and the external catalysis. Addition of PPDA with an appropriate concentration resulted a polymer with high polymerization degree and higher conductivity, which were closely related to the contribution of PPDA to the autocatalysis in the polymerization of aniline. Memory effects in and else properties of the catalytically electrosynthesized polyaniline were also studied.