CsI thin film photocathodes of 600 nm thickness deposited on polished Al surfaces by resistive evaporation technique were studied by angle-resolved X-ray photoelectron spectroscopy (ARXPS), before and after UV-irradiation under vacuum. It is shown that the "UV-irradiated" sample keeps the stoichiometric ratio Cs:1 unchanged (1:1) while it shows a higher concentration of carbon in comparison with "as-deposited" samples. The morphology of the "as-deposited" sample is strongly affected after VUV-irradiation. The consequence of such effects on the physical and chemical properties of the "as-deposited" and "UV-irradiated" CsI thin film photocathodes is discussed. (C) 2009 Elsevier B.V. All rights reserved.