The objectives of the present work were (1) to estimate the bioaccumulation of natural uranium (U) in a representative freshwater fish and (2) to assess the response of parameters involved in the defense against reactive oxygen species, in relation with the metal concentration and the exposure duration. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to a range of U concentrations in water (20, 100 and 500 μg U l-1) during 10 days. The activity of antioxidant enzymes superoxide dismutases (SOD) and catalase were measured in trout liver. In parallel, U analysis were performed in water and in trout gills. A significant accumulation of U occurred in trout gills in relation with the concentrations of U in water. SOD and catalase activities were both decreased by the exposure to U. U seemed to partly inhibit the antioxidant system of trout, indicating a potential enlarged sensitivity of exposed fish to oxidative damages.