Vacuum deposited polyaniline thin films have been found to exhibit a strong degree of non-linearity in the dielectric properties. As a function of change in the differential capacitance of metal-polymer-metal thin film capacitor upon application of d.c. bias. Dielectric capacitance and dielectric loss of the films were investigated in the frequency range from 10 Hz to 1 MHz, at different bias voltage. The above investigations lead to the estimation of charge carrier mobility, concentration, thin film crystallite size and diffusion constant in vacuum deposited polyaniline thin films. (c) 2006 Elsevier B.V, All rights reserved.