In this paper, decolourization of reactive red 35 was studied using advanced photo-oxidation process (UV/H2O2). The effect of operating parameters such as solution pH (3-11), H2O2 dosage (10-60 mM), and initial dye concentrations (100-200 mg/L) was studied on % decolourization. The operating parameters were optimized using response surface methodology. The global optimal parameters are: 46.6 mg/L of initial reactive red concentration, pH of 7.6 and H2O2 concentration of 20.5 mM.