Optimization of photocatalytic degradation of C.I. Basic Blue 3 (BB3) under UV light irradiation using TiO2 nanoparticles in a rectangular photoreactor was studied. The investigated TiO2 was Millennium PC-500 (crystallites mean size 5-10 nm) immobilized on non-woven paper. Central composite design was used for optimization of UV/TiO2 process. Predicted values of decolorization efficiency were found to be in good agreement with experimental values (R-2 = 0.9686 and Adj-R-2 = 0.9411). Optimization results showed that maximum decolorization efficiency was achieved at the optimum conditions: initial dye concentration 10 mg/L, UV light intensity 47.2 W/m(2). flow rate 100 mL/min and reaction time 120 min. Photocatalytic mineralization of BB3 was monitored by total organic carbon (TOC) decrease, and changes in UV-vis and FT-IR spectra. The photodegradation compounds were analyzed by UV-vis, FT-IR and GC-mass techniques. The degradation pathway of BB3 was proposed based on the identified compounds. (C) 2010 Elsevier B.V. All rights reserved.