Polypyrrole-polypropylene conducting polymer composite films with good mechanical properties and high electrical conductivity were prepared using a two-direction permeation/diffusion polymerization method. The oxidant used was iron(III) chloride. Polypropylene microporous films prepared by the biaxial stretching technique were used as the matrix material. The maximum conductivity of these composite films, 6.0 S cm(-1), is of the same order of magnitude as that of pure polypyrrole, 4.5 S cm(-1), which was synthesized by chemical oxidation of pyrrole monomer in aqueous solution. The composite films exhibit quite uniform mechanical properties in the film plane. Youngs modulus is in the range 0.4-0.8 GPa, tensile strength 40-85 MPa and elongation at break 90-200%, maintaining the mechanical properties of polypropylene in the composite. Polymerization conditions, including reaction time, reaction temperature and concentrations of the pyrrole and FeCl3 solutions, have a great influence on the structure and properties of the composite films. The structure of the conducting polymer in the composite films was characterized by X-ray photoelectron spectroscopy and the surface morphology of the films was investigated using scanning electron microscopy. Two kinds of surface structure were observed, one is a loose particle structure and the other is a compacted surface structure.