The method of surface plasmon resonance was used to determine the thickness, refractive index and extinction coefficient of thin electropolymerized films of polyaniline (PANI). A monotonic decrease of the refractive index (from 1.4 to 1.1) was observed in the thickness range of 5-20 nm. It stabilized at the level of 1.1 in the range of 20-30 nm. The extinction coefficient demonstrated similar behavior - its value reduced from 0.2 to 0.1 in the range of 10-30 nm. The optical parameters extracted by surface plasmon resonance are in good agreement with the data obtained using other optical methods. The nanocomposite model for formation of the electropolymerized PANI film was proposed. (C) 2007 Elsevier B.V. All rights reserved.