A facile approach for preparing flexible and conductive composite films by chemical polymerization of aniline monomers on the microporous polyacrylonitrile (PAN) surfaces was reported. A good adherence between polyaniline thin layer and PAN substrate was ascribed to the formation of a continuous conductive network in the film thickness along the capillary channel within PAN matrix. The electronic properties of the resulting composite films were tuned easily with the mass fraction of aniline monomer in the PAN solution or through chemical process. It is also found that the thermal stabilities of the composite films were significantly enhanced, while good mechanical properties were maintained.