The dielectric properties and ac electrical conductivity of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were investigated by using admittance spectroscopy (capacitance-voltage [ C-V] and conductancevoltage [G/omega-V]) method. These C-V and G/omega-V characterizations were performed in the frequency range of 1 kHz to 10 MHz by applying a small ac signal of 40 mV amplitude from the external pulse generator, whereas the dc bias voltage was swept from (-10 V) to (+10 V) at room temperature. The values of dielectric constant (epsilon'), dielectric loss (epsilon ''), dielectric loss tangent (tan delta), real and imaginary part of electrical modulus (M' and M ''), ac electrical conductivity (sigma(ac)), and series resistance (R-s) of the Al/PIN SBDs were found to be quite sensitive to frequency and applied bias voltage at relatively low frequencies. Although the values of the epsilon', epsilon '', tan delta, and R-s of the de-vice were observed to decrease with increasing frequencies, the electric modulus and sigma(ac) increased with increasing frequency for the high forward bias voltages. These results revealed that the interfacial polarization can more easily occur at low frequencies and that the majority of interface states (N-ss) between Al and PIN, consequently, contribute to deviation of dielectric properties of the Al/PIN SBDs. Furthermore, the voltage-dependent profile of both R-s and N-ss were obtained from the C-V and G/omega-V characteristics of the Al/PIN SBDs at room temperature. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 390-396, 2011