MgFe2O4 nanoparticles were hydrothermally synthesized at 150 ℃ using iron nitrate [Fe(NO3)3·9H2O], magnesium nitrate [Mg(NO3)2·6H2O] and sodium hydroxide (NaOH) as starting materials by carefully controlling the reaction conditions. The influences of several factors such as presence or absence of Na+, molar ratio of Fe3+ / Mg2+, concentration of mental ions, temperature and reaction time on resultant products were investigated in the hydrothermal process. The sample was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and its magnetic properties were measured using vibrating sample magnetometer (VSM).