Dielectric constant and conduction current of thin/ultrathinfilms of polyimides on substrates with thicknesses of 80-2000 nm were measured by using a small electrode system. Polyimides used in this study were poly(diphenylmethane-2,3,5-tricarboxycyclopentyl aceticimide, TCA-DDM) and poly(pyromellitic dianhydride oxydianiline, PMDA-ODA). With decreasing film thickness, the dielectric constant decreased but the conduction current increased. Using IR reflection absorption spectroscopy, we found that the polyimide chains are oriented parallel to the electrodes. The dependence of the dielectric constants on him thickness was explained by the orientation of polymer chains. (C) 2001 Elsevier Science Ltd. All rights reserved.