Ozonation of aqueous solution of Procion red MX-5B, a commercial azo reactive dye was investigated. The effect of various experimental variables on decolorization and degradation of the dye has been studied. Color removal was faster than organic removal. Dye mineralization was evident by the generation of oxalic and acetic acid during ozonation. The decolorization and organic removal chloride nitrate sulphate followed pseudo-first-order kinetics. Among the metal ions studied, manganese catalyzed ozonation showed better decolorization and organic removal. Fourier transform infrared (FTIR) spectroscopy results indicated the disappearance of bands for aromatics and appearance of bands due to carboxylic acids in the ozonated samples. Acetyl benzoic acid, diethyl phthalate and phthalic anhydride were identified as intermediates by gas chromatography mass spectra (GC/MS). Based on these findings a tentative pathway for the degradation MX-5B was postulated. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.