A co-doped polyaniline was prepared from aniline camphorsulfonate (ANICSA) and aniline hydrochloride (ANIHCl), which was soluble in common organic solvents, such as m-cresol. Without any additional doping, it possessed a higher conductivity (2 S/cm) than those prepared from ANICSA or ANIHCl alone (0.4 S/cm). In other words, a synergistic effect arose through the chemical oxidative polymerization of a mixture of ANICSA and ANIHCl. The mole ratio of (CSA + HCl)/aniline was 1; if additional HCl was introduced, the conductivity reached a value as high as 1.9 S/cm.