We prepared polycrystalline AgInSe2 thin films by vacuum evaporation on glass substrate at a high temperature using the stoichiometric powder. The thin films were characterized by X-ray diffraction and UV-vis-NIR spectroscopy. The samples were subjected to the irradiation of 1.26 MeV protons (H+). The effect of irradiation on the optical properties has been investigated for different doses of H+. It is observed that the band gap of silver indium selenide thin films decreases gradually with ion irradiation dose. (C) 2009 Elsevier B.V. All rights reserved.