The aim of this study was to determine the influence of various parameters such as the initial concentration of dye and catalyst, the volume of irradiated solution and its absorbance on the kinetics of photocatalytic degradation of azo-dyes. The studies were carried out in aqueous solutions containing the individual azo-dyes (Acid Black 1. Acid Orange 7, Basic Orange 66) and in their mixtures, in the presence of two types of TiO2 as photocatalyst and under UV light irradiation. It was found that under given experimental conditions, (lie photocatalytic degradation of investigated dyes exhibited pseudo first-order kinetics according to the Langmuir-Hinshelwood's heterogeneous catalysis model but only in the limited range of initial dyes concentrations. Moreover, the optimum TiO2 concentration, the pH value of zero charge point, the adsorption efficiency of dyes on catalysts and the optimum volume of irradiated solution were found. It was stated that in mixtures, dyes underwent photodegradation slower than in the one-component solutions. This phenomenon has been connected with the absorbance of irradiated solutions. (C) 2008 Elsevier B.V. All rights reserved.