Dielectric constant of indium-tin oxide (ITO) substrate was obtained by the basis of free electron model to evaluate the reflection infrared (IR) spectrum of an organic chin film on the ITO substrate in the wavenumber region from 3500 to 600 cm(-1). In a wavenumber region of less than 2000 cm(-1), the given spectrum was approximate to the spectrum on a metal substrate having high reflectivity. In this region. the thickness of the PVCz thin film under physical Vapor deposition process was proportional to the peal, intensity of reflection spectrum.