An effective and simple method was developed to prepare highly conductive polyaniline by coagulation polymerization. Depending on the coagulation reaction between aniline salts and lauryl sulfonate (SDS), not only was the polymerization rate of aniline monomers greatly decreased but also the doping efficiency of hydrochloric acid was effectively increased. Low polymerization rate provided enough time for the conformation adjustment of polyaniline chains and the diffusion of doping agent. Meanwhile, the doping efficiency of hydrochloric acid on polyaniline chains was effectively increased due to its easy diffusion among many vacancies, which were generated when SDS separated in the process of polymerization. Therefore, the electrical conductivity of polyaniline prepared by coagulation polymerization was increased more than ten times than that of polyaniline, which was prepared by conventional methods. In addition, the important factors to influence the preparation, such as SDS concentration, hydrochloride acid (HCl) concentration, content of ammonium persulfate (APS), and polymerization time were also investigated. When the molar ratio (aniline:SDS:HCl :APS) was set to 1.69:0.46:15.38:1, the conductivity of polyaniline reached 24.39 S/cm.