Thin films of tris-(8-hydroxyquinoline) aluminum (Alq(3)) were exposed to trace amounts of O-2, CO2, H2O, or to ambient air. Evolution of electronic structures of Alq(3) films with increasing gas exposure was measured using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy (XPS). The vacuum energy level, the highest occupied molecular orbital, and XPS core levels of the constituting elements in Alq3 shifted according to the kind of gas exposure. Chemical reaction between oxygen and the Alq(3) films was observed upon oxygen exposure. Moreover, it was found that the dominant influence of ambient conditions on the electronic structures of the Alq(3) films was from H2O.