The objective of this work was to study the abatement of 200 mg L-1 sulfamethoxazole (SMX) solution by means of photo-Fenton process. Biodegradability of the treated solutions was followed by the ratio biochemical oxygen demand at five days/chemical oxygen demand (BOD5/COD) and toxicity by Microtox (R) and inhibition tests. Experiments with different initial concentration of H2O2 were carried out. The initial amount of Fe2+ and pH of the solution were set at 10 mg L-1 and 2.8 respectively. The temperature of the reactor was kept constant in all the experiments (25 +/- 0.8 degrees C). Photo-Fenton process is thought to be a successful treatment step to improve the biodegradability of wastewater containing SMX. The complete antibiotic removal was achieved for a H2O2 dose over 300 mg L-1. Biodegradability (BOD5/COD) rose from zero (SMX solution) to values higher than 0.3 (treated solutions). Toxicity and inhibition tests pointed out in the same direction: oxidized intermediates for initial H2O2 dose over 300 mg L-1 showed no toxicity effects on pure bacteria and no inhibition on activated sludge activity. (c) 2007 Published by Elsevier B.V.