Cerium oxide nanoparticles (nCeO2) have been shown to have significant interactions in plants; however, there are limited reports on their impacts in rice (Oryza sativa). Given the widespread environmental dispersal of nCeO2, it is paramount to understand its biochemical and molecular impacts on a globally important agricultural crop, such as rice. This study was carried out to determine the impact of nCeO2 on the oxidative stress, membrane damage, antioxidant enzymes' activities, and macromolecular changes in the roots of rice seedlings. Rice seeds (medium amylose) were grown for 10 days in nCeO2 suspensions (0-500 mg L(-1)). Results showed that Ce in root seedlings increased as the external nCeO2 increased without visible signs of toxicity. Relative to the control, the 62.5 mg nCeO2 L(-1) reduced the H2O2 generation in the roots by 75%. At 125 mg nCeO2 L(-1), the roots showed enhanced lipid peroxidation and electrolyte leakage, while at 500 mg L(-1), the nCeO2 increased the H2O2 generation in roots and reduced the fatty acid content. The lignin content decreased by 20% at 500 mg nCeO2 L(-1), despite the parallel increase in H2O2 content and peroxidase activities. Synchrotron μ-XRF confirmed the presence of Ce in the vascular tissues of the roots.