The photocatalytic oxidation of an azo-dye acid black 1 (AB1) in water has been investigated over modified titanium dioxide (Tytanpol A11, "Police" Chemical Factory, Poland). The effect of operational parameters, i.e. pH of the solution, photocatalyst content, initial dye concentration on the photocatalytic process has been examined. It can be stated that the complete removal of color, after selection of optimal operational parameters, using modified Tytanpol A11 can be achieved in relatively short time, about 1 h. The catalytic material has been characterized by several analytical methods, like XRD, FTIR, UV-VIS/DRS. (C) 2002 Elsevier Science B.V. All rights reserved.