Abstract: Magnetic Fe_3O_4 nanoparticles were prepared first by co-precipitation method,and then magnetic Fe_3O_4 gelatin composite nanoparticles were prepared by the coacervated method using isopropanol as caocervation reagent.The effects of gelatin concentration,isopropanol volume and Fe_3O_4 content on particle size and properties were investigated.The average size of the composite nanoparticles was estimated from the measurement results of transmission electron microscopy(TEM) and zetasizer particle size analyzer;its structure and thermal stabilization were analyzed by X-ray powder diffraction(XRD),infrared spectroscopy(IR),thermogravimetry(TG) and differential thermal analysis(DTA).The results show that magnetic Fe_3O_4 gelatin composite nanoparticles is of a membrane enwrapping magnetic Fe_3O_4 nanoparticles structure with a small particle size and a favorable thermal stabilization.