The solid-state and electrochemical properties of potentiodynamically grown oxide thin films on indium were studied. The electrochemical characteristics of indium electrodes in 0.1 M Na-borate buffer solution; pH 10 have been correlated with the impedance spectroscopy results. The impedance spectra are interpreted in terms of an electrical equivalent circuit (EEC) based on a possible physical model, with the circuit elements representing electrochemical properties of indium and its oxide films. On the basis of the current, capacitance, resistance and Warburg impedance data, the potential regions where specific surface reactions occur could be delineated. The an odic behavior of indium was found to be under mixed control; the initial stage of an In oxide formation involves a faster charging process and a slower surface diffusion process, with an effective diffusion coefficient of the order of 10(-15) cm(2) s(-1). On the top of this layer, which is of monolayer dimensions, the growth of the barrier oxy-hydrate layer occurs via a base catalyzed hydrolysis of the surface oxide. Transformation from a gel-like oxide structure (InOOH) into the thermodynamically favorable and more stable crystalline form (In2O3) takes place at high positive potentials. In2O3 was found to expose high electric conductivity, which was manifested through oxygen evolution on its surface. Impedance spectroscopy was found to be a suitable technique for the complex structure characterisation of the surface layer formed anodically on indium,