The magnetic Co nanoparticle was prepared by coprecipitation route in aqueous solution and Figlarz’s polyol method which consists of refluxing a solution of the metal precursor in polyol. As the former method, the Co nanoparticle was synthesized by reduction of cobalt chloride with sodium borohydride in aqueous solution. And the latter method, the polyol method can be applied to the production of Co nanoparticle by reducing cobalt chloride and cobalt acetate with polyol such as ethylene glycol, trimethylene glycol. The size of nanoparticle was confirmed by transmission electron microscopy images and scanning electron microscopy images, according to the different methods The crystal structure of nanoparticle according to reaction condition was characterized by X-ray diffraction data. The magnetic properties were characterized with saturation magnetization from hysteresis loop by vibrating sample magnetometer (VSM).