Orange II, C.I. Acid Orange 7 (AO7), is oxidatively decolorized via catalytic oxidation by iron(III) phthalocyanine-tetrasulfonic acid (Fe(III)-PcTS) as a biomimetic catalyst and KHSO5 as an oxygen donor. The nature of the decolorization of AO7 was investigated in the catalyst concentration range of 10-50 muM, in which the initial concentration of AO7 was 417 mg l(-1). A 99.6% decolorization was observed at [KHSO5] = 2.5 mM and [Fe(III)-PcTS] = 20 muM after a 3-h reaction period. However, the fact that only 4.9% of the TOC was removed indicated that the conversion to CO2 was incomplete. The results of a total organic nitrogen analysis of the reaction mixture showed that the nitrogen in the azo chain was mainly converted to N-2 gas. In addition, 38.6% of the AO7 was converted to 1,2-dihydroxynaphthalene, and 21.4% to p-phenolsulfonic acid. These results indicate that the degradation via this catalytic system involves the conversion of AO7 to phenolic compounds, followed by N-2 production. In addition, a Microtox test showed that toxicity of the solution increased as a result of AO7 oxidation using this catalytic system. (C) 2004 Elsevier B.V. All rights reserved.