Polyaniline (PAn) emeraldine salts (PAn-Cl, PAn-Br, PAn-ClO4) were synthesized by the electrochemical method using different acids (HCl, HBr, HClO4). PAn salts in pellet form were used as sensors for organic ( EtOH,CHCl3,C6H6) and inorganic ( HCl, NH3) solvents. Electrical conductivity responses of PAns to five solvents were investigated. The change of electrical conductivity of PAns (Delta sigma), relative to the value measured before exposure, varied with the solvent used. The sensor properties of PAns varied depending on the nature of dopant anions such as the type and size. It was found that PAn-ClO4 has the highest sensing power on HCl, NH3, and CHCl3, and it has the lowest sensing power on C6H6.