Near monodisperse Fe₃O₄ sub-microspheres with an average diameter of 170 nm have been synthesized by a solvothermal reduction method, using K₃[Fe(CN)₆] as the raw material in the absence of any surfactants at 200°C for 24 h. The products were detected by XRD, FESEM, TEM, and XPS. The investigation of the reaction parameters indicates that ethylene glycol plays a key role both as reducing agent and solvent. In addition, the reaction time and temperature also have important influences on the final product. The hysteresis loop of the near monodisperse Fe₃O₄ sub-microspheres shows a ferromagnetic behavior with saturation magnetization of 60.8 emu/g and coercivity of 124.7 Oe.