Pure nano-crystalline Co powders of nearly spherical shape have been produced using a high-energy ball mill. This method has used the mechanical force to crush solid reactant, which increased the BET specific surface area and reaction speed of reactant, and accelerated the nucleation rate. The method includes three steps. Firstly, a precursor of CoC2O4 was prepared by the mechano-chemical solid state reaction with H2C2O4·2H2O and Co(NO3)2·6H2O at ambient temperature. Secondly, the precursor CoH2C2O4 powders were dispersed by spray-drying to get the spherical precursor. Finally, Co powders were obtained by decomposition of the precursor CoH2C2O4 for about 3~3.5 h at 450~500 oC. The powders were characterized by X-ray diffractometer and scanning electron microscopy. The results show that spherical, cubic structure, 100 nm β-Co powders were synthesized