Degradation and mineralization of Calcon, an azo dye in aqueous solution were studied, probably for the first time using UV365/H2O2 technique at various pHs. Higher degradation of Calcon is achieved in strong basic medium (99.4% at pH = 12.6 at 1260 mu W cm(-2)) than in strong acid medium (approximate to 96% at pH 1.0 and 3.0 at 1260 mu W cm(-2)) both in the presence and absence of H2O2. Higher degradation under strong alkaline medium may partly be attributed to the neutralization of the acids formed in the mineralization process and partly to the involvement of additional HO. radicals. The high degradation in the absence of H2O2 under strong acidic medium may be attributed to the role played by the counter ion of the acid used for adjusting the pH; SO42- in the present case. The degree of mineralization is more in the presence of H2O2 than in its absence and is pH dependent (pH 1 > pH 12.6 > pH 3). The results show that strong acidic and basic media favor degradation and that mineralization of dye molecules in neutral form is more favored than in anionic form. (C) 2011 Elsevier B.V. All rights reserved.