The effect of Au, Ag, Cu and Ni nanoparticles deposited on TiO2-P25 was studied on the photodegradation of trimethoprim, a commonly used antibiotic. The synthesized materials were characterized by ICP, EDS, XRD, BET, UV-vis, TEM and TPR. The metal loading was 0.5 wt.% and the average particle size was about 2 nm in all the studied samples. The deposition of metallic particles on TiO2-P25 produces an enhancement of the activity of the bare semiconductor; when the degradation of trimethoprim was carried out by pure TiO2-P25, the mineralization reached only 50% of the organic matter, while by using metallic nanoparticles deposited on TiO2-P25, the mineralization of organic matter increased up to 80% for the same reaction conditions and reaction time. The evaluation of the photocatalytic activity was made for solutions containing trimethoprim in concentrations of 40 ppm under UV light irradiation using a lamp with primary emission at 254 nm and 2.2 mW/cm(2). It is shown that the ability of the photocatalyst to mineralize trimethoprim depends on the electron affinity and the electronegativity of the deposited metal. (C) 2013 Elsevier B.V. All rights reserved.