Cadmium oxide (CdO) thin films have been deposited by reactive dc magnetron sputtering on to glass substrates at room temperature and subsequently annealed at 275 degrees C for 3 h in vacuum. The as-deposited and annealed films were characterized for their structural and optical properties. The films were also tested for hydrogen sensing at different operating temperatures. The annealed samples showed better response down to 50 ppm at a relatively low operating temperature of 100 degrees C. The role of non-equilibrium surface states as a possible sensing mechanism is explained. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.