Polyaniline/polypropylene composites were prepared by oxidative polymerization of aniline in biaxially stretched polypropylene microporous films with ammonium persulfate as the oxidant. A continuous permeation/diffusion polymerization process was used in order to incorporate more polyaniline in the composite. The influence of reaction time and temperature and the concentration of monomer and oxidant aqueous solutions on the electric conductivity of the composites was investigated. The composites may exhibit a loose particulate surface morphology and a compact surface with a ring-shaped structure. The content and distribution of polyaniline in the composite and, hence, its electric conductivity and surface properties can be controlled over a wide range. Composites with the combination of high electric conductivity and good mechanical properties can be obtained under proper conditions. The composite films were flexible and strong enough and have electric conductivity as high as 5-6 S/cm.