Polyaniline (PAn) can be doped through a protonation by protonic acids, in addition to an oxidation doping by Lewis acid as for the other conjugated conducting polymers. This work reports the new class of dopant, ionic salt, such as LiClO4, LiBF4, LiPF6, and Zn(ClO4)(2), for PAn. The ionic salt can be used to dope PAn by mixing an ionic salt with PAn in the common solvent 1-methyl-2-pyrrolidone and then casting the solution into a film. The structure and properties of ionic salt doped-PAn are investigated by UV-visible, IR and XPS spectroscopies, dynamic mechanical analysis, scanning electron microscopy, and conductivity measurement. It is found that the PAn therein is doped via pseudoprotonation of the imine nitrogen by the metal cation. As in the case of HCl-doped PAn, polarons/bipolarons are generated as reflected in the presence of UV-visible absorption peaks at 420 and 865 nm. The LiBF4-doped PAn film retains a conductivity at the level of 10(-2) S/cm in the temperature range 25-140 degrees C. The conductivity then decays to 10(-3) S/cm as temperature increases to 175 degrees C, resulting from the increased ring distorsion in the PAn subchains due to the glass transition.