Magnetic Fe 3 O 4 nanoparticles were prepared by carbothermal reduction using solution combustion synthesis precursors derived from ferric nitrate (oxidizer), glycine (fuel) and glucose (carbon source) mixed solution. In this paper, the growth mechanism and magnetism in Fe 3 O 4 nanoparticles were investigated by adjusting the glucose content in precursor and the heat temperature in carbothermal process. The products were analyzed by X-ray diffraction, Field emission scanning electron microscopy, Infrared adsorption method and Vibrating sample magnetometry. The results revealed that the more amount of glucose, the earlier Fe 3 O 4 phase generated as temperature increasing. Depending on glucose content and thermal temperature, the average grain size of Fe 3 O 4 nanoparticles varied from 19.9 nm to 48 nm and saturation magnetization changed from 21.2 emu/g to 71.77 emu/g, which indicated that the saturation magnetization of Fe 3 O 4 nanoparticles fell off as the average grain size decreasing. These results were crucial not only from the application stand-point, but more importantly leaded to a new platform for further studies of high quality magnetic Fe 3 O 4 particles at nanoscale. [ABSTRACT FROM AUTHOR]