The photooxidative decolorization of C.I. Basic Yellow 2 (BY2), was investigated using UV radiation in the presence of peroxydisulfate (S2O82-) in a rectangular photoreactor at experimental condition. S2O82- and W-light showed negligible effect when they were used independently. Removal efficiency of BY2 was sensitive to the operational parameters such as initial concentrations Of S2O82-, BY2, light intensity, flow rate and pH. The conversion ratios of BY2 at the volumetric flow rates of 330, 500 and 650 ml/min were 84%, 79%, 51% in 30 min, respectively. Our results showed that light intensity was a beneficial parameter for dye removal. The results showed that in the presence Of S2O82-, the photooxidation quantum yield obtained was higher than direct photolysis quantum yield, suggesting that photodecay of BY2 was dominated by photooxidation. The electrical energy per order (E-EO) values for decolorization of BY2 solution was calculated. Results show that applying a desired peroxydisulfate concentration can reduce the E-EO. (C) 2008 Elsevier B.V. All rights reserved.