Residues of veterinary antibiotics in wastewater from breeding farms can be degraded effectively using the photocatalytic process. The aim of this study was to assess the changes in the biodegradability and antimicrobial activity of solutions containing ampicillin, doxycycline, tylosin or sulfathiazole after the photocatalytic process. The antimicrobial activities of the initial antibiotic solutions and the photocatalytic degradation products of these drugs were determined relative to eleven taxonomically diverse microbial species: Microbacterium spp, Brevundimonas diminuta, Citrobacter freundii, Comamonas testosterone, Enterococcus casseliflavus, Delftia acidovorans, Kurthia gibsonii, Staphylococcus warneri, Pseudomonas aurantiaca, Serratia rubidaea and Pichia anomalia. In contrast to the initial antibiotics, the photodegradation products were biodegradable. The important conclusion of this research is that partial photocatalytic mineralization of each of the studied antibiotic solutions resulted in the complete disappearance of their antimicrobial activity against the tested microorganisms. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.