This work studied the photocatalysed oxidation of the antibiotic oxolinic acid (OA) in an annular reactor operated with immobilized TiO2 on sintered glass cylinders (SGC). Experiments were carried Out in I I solution of OA (18mg 1(-1)) at pH 9 with oxygen bubbling. Irradiation was performed with black light (36 W). The reaction was monitored by COD, TOC and average oxidation state (AOS) calculations. The antibacterial activity of intermediates was followed using the inhibition halo technique on Escherichia coli cultures. The initial antibiotic concentration decreases in one order of magnitude after 60mm irradiation. and was completely eliminated at 100min reaction. The TOC was reduced in 54% and the AOS reach Values around +3 indicating the formation of low molecular weight carboxylic acids. The oxidation reaction fit well with the Langmuir-Hinshelwood kinetic model indicating the dependence of reaction rate with initial adsorption step. The antibacterial activity of the Solution decreases with antibiotic removal. demonstrating that intermediates do not present antibiotic activity. (C) 2008 Elsevier B.V. All rights reserved.