Carbon-encapsulated Cobalt nanoparticles were synthesized with sucrose as carbon source and cobalt nitrate as metal source in nitrogen atmosphere. The weight of purified sample could arrive around 12-20 grams at one time. The as-prepared CECNPs sample was characterized by transmission electron microscopy (TEM), X-ray diffraction technique (XRD), vibrating sample magnetometer (VSM) and Raman spectroscopy. The results showed CECNPs was typical core / shell structure on nanometer scale, the core was cobalt single crystal, the shell was graphitic carbon, and the particle size was about 30nm. The magnetic measurement revealed that CECNPs was ferromagnetic material with the quite small remanent magnetizations Mr of 3.7emu/g and coercive forces Hc of 275Oe at room temperature.