The nanosized thin layers (about 1-2 nm) between the indium tin oxide crystalline films and glass substrates were studied using photoinduced optical and second-order nonlinear optical [second-harmonic generation (SHG)] effects. Photoinduced changes of the effective energy gap were found for the first time in the In(2)0(3) films doped by different amount of Sn deposited on the glass substrates. The photoinduced second-order susceptibilities show, a good correlation with the behavior of the fundamental absorption edge. The maximal SHG response of the photoinduced signal was observed for a pump-probe delay times equal to about 26 ps. The experimental measurements indicate that the observed effects are stimulated by two factors: the first factor is related to the interface potential gradients on the border glass interface. The second factor is a consequence of the additional polarization due to insertion different amount of Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigations of thin semiconducting-glass interface layers. (C) 2003 American Vacuum Society.