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.