The photodegradation of an industrial azo dye C.I Basic Red 46 was examined in a fixed-bed photoreactor using UV-lamps simulated to the solar irradiation. In our photodecolorization study, the UV/TiO2 process was optimized using the Box-Behnken approach to evaluate the synergistic effects of three independent parameters (initial concentration of the dye, flow rate, and UV intensity) on mineralization effectiveness. The response surface methodology was in good promise with the prediction model (coefficients of determination of decolorization and mineralization were R-Dec(2) = 0.997 and R-TOC(2) = 0.994, respectively). The effects of the factors could be estimated from a second-order polynomial equation and student's t-test. The optimal parameters of decolorization and mineralization were as follows: initial concentration of colorant 25 mg L-1, rate of fluid flow 0.3 L min(-1), and ultraviolet light intensity 38.1 W m(-2). The decolorization and mineralization removal efficiency under these optimal conditions were 100% and 57.63% respectively. These results indicate that optimization using response surface methodology, based on the Box-Behnken approach, is an excellent tool for determining the optimal conditions, and the process can be easily extrapolated for a specific treatment of real waste water containing the azo dye C.I Basic Red 46. Also, the intermediates that were produced during photodegradation process of Basic Red 46 were determined by GC/MS. (C) 2020 Published by Elsevier B.V. on behalf of King Saud University.