Near monodisperse Fe 3 O 4 sub-microspheres with an average diameter of 170 nm have been synthesized by a solvothermal reduction method, using K 3 [Fe(CN) 6 ] as the raw material in the absence of any surfactants at 200℃ 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 Fe 3 O 4 sub-microspheres shows a ferromagnetic behavior with saturation magnetization of 60.8 emu/g and coercivity of 124.7 Oe. solvothermal, sub-microspheres, morphology, saturation magnetizationIn recent years, increasing attention has been paid to the morphology and size control of materials synthesized on the micro-and nano-scale due to the fact that morphology and size play very important roles in determining chemical and physical properties of materials. As a type of important functional materials, iron oxides such as γ-Fe 2 O 3 and Fe 3 O 4 are becoming more and more attractive because of their intrinsic half-metallic ferromagnetic nature, which can be widely used in catalysts, biological assays, chemical sensors, ferrofluids, colored pigments, high density magnetic recording media, super paramagnets, etc. [1][2][3][4][5][6][7] . Because of the widespread applications, much attention has been paid to the preparation of different kinds of magnetic nanoparticles in the past dozens of years. To date, a number of preparation methods for magnetic nanoparticles have been developed, such as chemical co-precipitation [8] , oil-in-water emulsion [9] , sonochemistry [10] , spray pyrolysis [11] , hydrothermal [12] , solvothermal [13] , arc-discharge [14] , combustion synthesis [15] and thermal decomposition [16] . Although magnetic particles with narrow size distribution have been synthesized by various methods since the fabrication of monodisperse magnetic nanoparticles reported by Matijeviae in the early 1980s [17,18] , the products were overwhelmingly dominated by particles with sizes of dozens of nanometers. With the development of the modern science, it is an interesting challenge to develop approaches to synthesize magnetic particles with suitable sizes to meet the special need of biomedical fields. The research results indicate that various magnetic nano-or micro-particles have been considered as ideal candidates for biological applications such as protein and enzyme immobilization, cell isolation, DNA and RNA purification, immunoassay and guided site-specific drug delivery [19][20][21][22][23] , due to their good hydrophilic and biocompatible properties.Various chemical synthetic routes have been developed to synthesize monodisperse magnetite (Fe 3 O 4 ) particles. The main difficulty in synthesizing monodisperse Fe 3 O 4 particles is the intrinsic agglomerating properties of magnetic nanoparticles. Recently, in order to prevent this agglomeration, the synth...

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