The microstructures of chemically polymerized polypyrrole films (100-800 Å thick) were studied by transmission electron microscopy, electron diffraction, and x-ray photoelectron spectroscopy. In contrast to previous work where only amorphous polypyrrole was found, crystalline fiber structures were observed in the chemically polymerized thin films. The fibers are embedded in an amorphous matrix which forms a self-reinforced composite. The shape of the fibers ranged from thin rods to ellipsoids depending on the preparation conditions. The density and size of the fibers were affected by the polymerization time and the concentration ratio of pyrrole and oxidants. Polypyrrole fibers were aligned along the thin-film plane and were randomly oriented in the plane. The two-dimensional orientation of the crystalline fibers produced strongly anisotropic electrical properties in the thin films.