The photocatalytic oxidation of phenol in water in the labyrinth flow reactor with immobilized catalyst bed was investigated. Degussa P25 was used as a photocatalyst. It was observed that the photocatalytic material considerably losses its activity during repeated test trials for the high initial phenol concentration of 300 mg/dm(3). Diffuse reflectance UV-Vis analysis showed shift in the threshold absorption value and corresponding band gap energy of the photocatalytic material. FTIR analysis revealed the carbon deposits on the catalyst surface. These two factors are considered to be responsible for the activity decrease. (C) 2003 Elsevier B.V. All rights reserved.