The process of removal of two azo dyes (Reactive Red 198 and Direct Green 99) from water was investigated. The adsorption of azo dyes onto surfaces of pristine TiO2, P25 and carbon-modified TiO2 (at 120 degrees C for 24 h) was presented. The Freundlich model of adsorption isotherm was found for pristine TiO2 and TiO2-P25. Modification of TiO2 by carbon lead to the change from the Freundlich model to the Langmuir model of adsorption isotherm. For the TiO2-C photocatalyst the adsorption capacity was determined, which was almost two times higher for Direct Green 99 than Reactive Red 198 dyes. As a result we observed the increase of photocatalytic activity of carbon-modified TiO2 photocatalyst. (C) 2009 Elsevier B.V. All rights reserved.