Electrochemical oxidative polymerization of m-phenylenediamine (mPD) gave a nonconducting limited-thickness polymer film on the gold electrode. To obtain new functional films for surface modification, the electrochemical copolymerization of aniline (An) and mPD at different ratios of the monomers was performed by potential scanning between -0.1 V and 0.92 V (vs. see). With quartz crystal microbalance measurements, the growth rate of the film and the amount of protein cross-linked on the polymer film were investigated. The results showed that a - NH2 functionalized film could be obtained by the copolymerization of An with mPD at appropriate monomer ratio, and that the precoated poly-An film enhanced not only the depositing rate of poly-mPD but also the immobilizing capacity of the poly-mPD film remarkably.