Four different magnetic Fe 3 O 4 nanoparticles were synthesized and characterized by solvothermal method based on different sodium salts. Sodium salts which were used to synthesize the nanoparticles were NaOAc, Na 2 CO 3 , a mixture of NaOAc and Na 3 Cit, and a mixture of NaOAc and Na 2 C 2 O 4 . The structural and optical properties of the synthesized nanoparticles were examined by XRF, XRD, SEM and FT-IR. The results estimated from XRD pattern and SEM image indicated that the second sample (Na 2 CO 3 ) had the lowest average particle and crystallite size around 29 nm and 43 nm. It was also shown that the first (NaOAc) and second (Na 2 CO 3 ) samples had the best FT-IR spectra, similar to the available commercial sample which was provided by Merck. At last, the prepared Fe 3 O 4 nanoparticles were applied as sorbents to sorb uranium ions (U(VI)) from radioactive wastewater. The adsorption results showed that the highest U(VI) adsorption was obtained for the second sample in the solution with pH around 10.