Abstract: Infrared spectrum, X-ray diffraction, transmission electron microscopy and conductivity measurement were employed to investigate the properties and structure of polyaniline samples, which were synthesized by emulsion polymerization with different concentrations of ammonium peroxydisulfate and dodecyl-benzene sulphonic acid. The electrical conductivity of polyaniline varied with the molar ratio of oxidant and doping agent to aniline and reached peak at some value, while some characteristic peak values at their infrared spectrum changed their location and intensity relatively. The crystallization degree of different samples exhibited distinction due to different synthesis conditions. Under the optimum synthesis condition, a fibril morphology and higher crystallinity were observed. The results indicate that the change of oxidation and doping condition affects the ratio of benzenoid to quinoid ring and the orientation order of the polyaniline chain, which are important factors to decide the conductivity of polyaniline.