The electropolymerization and doping/dedoping properties of polyaniline ultrathin films on Au electrode surfaces were investigated by a combination of in situ electrochemical techniques, i.e., electrochemical surface plasmon spectroscopy (ESPR) and the electrochemical quartz crystal microbalance (EQCM). In the ESPR measurements, we employed two wavelengths, i.e., 632.8 and 1152 nm in order to distinguish independently the electrochromic behavior. In addition, we used spectroelectrochemical transmittance measurements in order to probe further the optical properties of the polymer films as a function of the applied potential. The real and imaginary parts of the dielectric constant of the polyaniline thin film at several doping levels was determined quantitatively by taking into consideration the thickness values obtained from the EQCM measurement. The combination of these two techniques provides a powerful method for probing the electrical, optical, and dielectric properties of conjugated ultrathin polymer films.