Ultrathin films were formed from two types of non-conjugated polyelectrolytes, that is, polyallylamine (PAH) and polystyrensulfonate (PSS) using a self-assembly process and their electrical properties were investigated. Current versus voltage properties of the devices showed hopping conduction. The conduction was considered to be due to the migration of mobile ions in the sample, and that was also supported by temperature and humidity dependence of transient currents. Furthermore, thermally stimulated currents (TSCs) properties also suggested the ionic space charge polarization. Although the origin of mobile ions is not yet clear, the existence of sodium in the films was observed from the electron spectroscopy for the chemical analysis (ESCA). The humidity (i.e. water in the devices) also had a great influence on the electrical properties. The sodium ions and/or oxonium ions in the device are considered mobile ions. (C) 1998 Elsevier Science S.A. All rights reserved.