Electrically conductive films were prepared by copolymerization of pyrrole (Py) and 2-formyl pyrrole (FPy) in the presence of trifluoroacetic acid (TFA) used as a catalyst in chloroform. Formation of the copolymer P(Py-co-FPy) films was examined, when the FPy monomer mole fractions was changed. The obtained films showed a metallic greenish black color and had electrical conductivity of 10(-4) to 10(-1) S/cm when I-2 was doped in the copolymer films. As the mole fraction of the FPy increased from 0 to 0.5, the tensile strength of the films increased from 11.1 to 81.3 N/mm(2). For analysis of the copolymerization, NMR in deuterated chloroform was measured and the evidence was revealed that the formyl group of FPy was attacked by the acid catalyst before the copolymerization started.