Polyaniline (PANI) samples were synthesized by an ultrasonic irradiation synthesis method and by a magnetic stirring process. The structure of the polyanilines Was investigated by using infrared and UV-vis-NIR spectral analysis, X-ray diffraction, transmission electron microscopy, electron diffraction, and elemental analysis. The results clearly show that the crystallinity of polyaniline synthesized by using the ultrasonic synthesis method is much higher than that synthesized by the stirring synthesis method under similar conditions. Transmission electron microscope observation shows that the polyaniline powder synthesized by. using the ultrasonic method consists mainly of hexagonal plates: Electron diffraction, results show that the plates are small single crystals with well-developed hexagonal morphology. The lattice parameter of the crystal is a = b = 4.56 Angstrom. A network structure model of crystalline polyaniline is proposed. The results of elemental analysis and the solubilities of the two types of PANI support this model. The conductivity and thermopower of polyaniline synthesized by the ultrasonic method are lower than the same properties exhibited by samples synthesized by the conventional method. The results indicate that polyaniline with higher crystallinity does not possess higher conductivity.