The radiolysis of a variety of iron oxide powders with different amounts of associated water has been performed using γ rays and 5 MeV (4)He ions. Adsorbed water was characterized by both temperature-programmed desorption and diffuse reflection infrared Fourier transform spectroscopy to reveal a variety of active sites on the surface. Molecular hydrogen production was found only from water adsorbed on Fe2O3, and the yield was several orders of magnitude greater than that of bulk water. Aqueous slurries of FeO, Fe3O4, and Fe2O3 examined as a function of water fraction gave different yields of H2 depending on the oxide type and the amount of water. Examination of the iron oxide powders following irradiation by X-ray diffraction showed no change in crystal structure. Raman spectroscopy of the oxides revealed the formation of islands of Fe2O3 on the surfaces of FeO and Fe3O4. X-ray photoelectron spectroscopy of the oxides revealed the general formation of oxygen species following radiolysis.