Quartz crystal microbalance(QCM) was used to study the autocatalytic polymerization of aniline. The deposition of polyaniline film via autocatalytic polymerization onto a Pt quartz crystal causes the decrease in oscillation frequency of the crystal in QCM, thereby the mass of the film is determined. The experimental results show that the catalytic activity of Pt substrate is much stronger than that of the polyaniline film on the autocatalytic polymerization. The rate of the autocatalytic polymerization falls down gradually with the time and reaches a steady value finally. The film can reach about 0 17 μm after 24 hours deposition.