An advanced measuring system was developed using quartz crystal analyzer (Q.C.A.) for the in-situ measurement of the resonant frequency and resonant resistance of the polypyrrole deposited Q.C.A. with electrochemical reaction. The system was used to monitor polypyrrole deposition by the constant current method. In the electrochemical deposition, not only the resonant frequency change but also the resonant resistance increase was observed. The elastic film is formed at first stage of polymerization, but transformed to viscoelastic film later and this procedure is repeated in the process of polymerization.