An optimal condition applied to the Taguchi method with an 1.9 orthogonal array for preparing a visible-light driven nitrogen-modified TiO2 (N-TiO2) photocatalyst by a simple hydrolysis method has been examined for material characteristics and a photodecolorization test of methyl blue (MB) under various visible light source (fluorescent and blue LED lamps) irradiations. Results of the material characterization showed that the absorption of prepared N-TiO2 powder exhibited a significant extension into visible light regimes with an optical bandgap (Eg) of around 2.96 eV, which subsequently improved the visible-light photocatalytic activity of N-TiO2 samples. The superior photocatalytic properties, the pseudo first-order reaction rate constants (k) and photodecolorization efficiency ON of a N-TiO2 photocatalyst during the photodecolorization test of methyl blue (MB) under two different visible light irradiations were very evident compared to those for pure TiO2. For photodecolorization of practical dyeing from the waste water from the dyeing and finishing industry, a higher photodecolorization efficiency of N-TiO2 powder toward Direct blue-86 (DB-86) (Direct Fast Turquoise Blue GL) dye was also achieved. (C) 2011 Elsevier B.V. All rights reserved.