Impedance spectroscopy and cyclic voltammetry measurements were used to examine solid-slate properties of thin anodic films on tin. The impedance of tin \ n-type SnO2 \ electrolyte system was studied as a function of applied potential and frequency. In the absence of illumination at room temperature. the impedance spectroscopy technique when used in conjunction with an applied bias potential can be a powerful tool for identification of deep-level states. An electrical equivalent circuit corresponding to the Voight model, which describes the behavior of the passive film on tin more adequately than the models for ＇classical＇ semiconductors, is presented. The change in the Mott-Schottky plot was interpreted in terms of partial ionization of deep-level states. The resistive component of the impedance measured at low frequencies was much more sensitive to deep-level states than the capacitive one and was used to determine their distribution in the bulk of SnO2. Both flat-band potential and donor concentration were estimated from the space charge capacitance at high frequencies. The dielectric properties of the oxide film were discussed and several parameters were determined in terms of a parallel plate capacitor and in accordance with the high-field growth law.