The electrochemical polymerization of aniline via cyclic voltammetry (CV) was performed in 1 M HCl and 0.2 M aniline solutions with various concentrations of IrCl3. xH(2)O. The rate of polymerization strongly depends on the concentration of IrCl3. xH(2)O and reaches a maximum at 0.2 mM IrCl3. xH(2)O on the basis of the anodic peak current at ca. 280 mV (peak A(1)). The electrochemical properties of Ir-doped polyaniline (PAN) films for the application of electrochemical (EC) capacitors were characterized by their i-E and chronopotentiometric responses in 0.5 M H2SO4. The effect of iridium oxide on the chemical environments of PAN was demonstrated by X-ray photoelectron spectroscopy (XPS). Morphologies and crystalline structures of these Ir-doped PAN films are, respectively, examined by scanning electron microscopic (SEM) photographs and X-ray diffraction (XRD) patterns.