The production of reactive oxygen species (ROS) and the induction of the antioxidative defense mechanism are very important in heavy metal toxicity. In this study, biological effects induced after uranium contamination were investigated for Arabidopsis thaliana. Three-week-old seedlings were exposed for 4 days to 100 µM U in an adjusted Hoagland solution. Uranium exposure caused a decreased growth of leaves and roots and a modified nutrient profile was observed. Investigation of lipid peroxidation products indicated an increase of membrane damage. Important ROS-producing and -scavenging enzymes were studied at transcriptional and protein level to investigate the importance of the ROS-signature. Elevated gene expression was observed for a ROS-producing enzyme. Changes in gene expression for different ROS-scavenging enzymes were observed. Higher ascorbate levels in uranium exposed leaves suggested an increase of antioxidative defense via the ascorbate-glutathione pathway. Precipitation tests recommend the use of 25 µM P in combination with 100 µM U to inhibit uranium-phosphate precipitation. The influence of this low phosphate concentration on plant growth and oxidative stress had to be evaluated. Minor differences between low phosphate (25 µM P) and high phosphate (100 µM P) treatments were observed justifying the use of the low phosphate concentration in combination with uranium.