The kinetics of decolorization of Malachite Green (MG) as a model cationic dye from textile industry, by US/UV/H2O2 process, was investigated with nonlinear regression analysis. The experimental results indicated that the decolorization kinetics of MG in this process fit well by pseudo-first order kinetics. With nonlinear regression analysis a model was developed for pseudo-first order constant (k(ap)) as a function of operational parameters such as initial concentrations of H2O2 (25-600 mg l(-1)) and MG (1.82-9.87 mg l(-1)), temperature (294-307 K) and power density (0.049-0.16 W ml(-1)) as following: k(ap) = 283 exp(-9000/RT)(0.0205 + (1.76 x 10(-3)[H2O2](o)/1 + 4.86 x 10(-4)[H2O2](o) + 9.5 x 10(-6)[H2O2](o)(2))[MG](-0.668)(P/V)(0.313) For electrical energy cost evaluation, the figure-of-merit electrical energy per order (E-EO) was estimated from experimental and theoretical data. The results show that EEO is very sensitive to the mentioned operational parameters. (C) 2009 Elsevier B.V. All rights reserved.