Chromium oxide nanocrystallites have been synthesized by thermal decomposition of solid precursors and evaluated as catalysts for ammonia decomposition. The physical and chemical properties of Cr2O3, catalysts are characterized by various techniques such as N-2 adsorption-desorption isotherms, XRD, TEM. and XPS. The relationship between catalytic activities and physicochemical and electronic properties of Cr2O3 catalysts is investigated. The Cr2O3 catalysts are active for ammonia decomposition and the activity is structure-sensitive with a close relation to particle size. During the ammonia decomposition reaction, N atoms are inserted into the Cr2O3 catalyst thus enhancing the activity of catalyst, due to the variation in the physical, chemical and electionic structures of Cr2O3 catalysts. (C) 2009 Elsevier B.V. All rights reserved.