Decolorization of reactive azo dye, reactive black 5 (RB5), was conducted using Fe(III) immobilized on Montmorillonite K10 (MK10) as a catalyst in the presence of H2O2 using Fenton-like oxidation process. The effect of different parameters such as iron ions loading on supported catalyst, catalyst dosage, initial pH of dye solution, initial concentration of H2O2 and dye and reaction temperature on the decolorization efficiency of the process were studied. The results indicated that by using 12 mM of H2O2 and 3.50gL(-1) of the 0.11 wt.% Fe(III) oxide on MK10 catalyst at pH of 2.5, 99% of decolorization efficiency was achieved within 150 min in a batch process. (C) 2009 Elsevier B.V. All rights reserved.