In this article, by using surface I-V and C-V characteristics, the levels of moisture uptake and the degree of surface polarization were studied on the newly developed all-aromatic and aromatic/aliphatic copolyester thermosetting thin films with a thickness of 1.0-5.0 mu m. The all-aromatic copolyester films which contain more rigid structures appear less polarizable and less hygroscopic compared to aromatic/aliphatic copolyester. It was also found that both the surface current leakage and the polarization are lower than those of the commercially available polyimide systems. The data suggested three types of moisture which could be described by the dehydration conditions required to restore original C-V characteristics. The effects of curing conditions on moisture absorption and polarization are also presented.