Photo-oxidation of NH3 (photo-SCO) takes place at room temperature over TiO2 photocatalyst. From the results of photo-SCO reaction over various TiO2, we found that JRC-TIO-8 exhibited the best activity and 100% NH3 conversion was achieved at GHSV = 25,000 h(-1). ESR study revealed that the photo-SCO proceeds by the reaction between NH2 radical and oxygen anion radical species. We found that the photo-SCO activity correlated to the amount of the NH3 chemisorption amount of TiO2 and the oxygen anion radical species. In particular, the produced amount of O-3(-) radical is more active in the photo-SCO. (c) 2006 Elsevier B.V. All rights reserved.