In this work, redox states and speciation of U in U coprecipitated with and sorbed on magnetite nanoparticles are investigated by U M₄ HR-XANES, L₃ EXAFS, XPS and TEM techniques. Coexistence of U(V), U(IV) and U(VI) in varying ratios is clearly detect by the U M₄ HR-XANES technique. Mainly U(V) stable for more than 240 days of contact time is found In a coprecipitated sample with lowest U loading (1000 ppm U). Coprecipitated sample with highest U loading (10000 ppm) undergoes reduction to U(IV) within less than 7 days. Reduction kinetics of U and long term stability of U(V) is discussed for both batch sorption and coprecipitation systems.