Nonaggregate and well-crystallized Co 3 O 4 nanoparticles with size of 5–15 nm were prepared on a large scale at low temperature by an epoxide precipitation route. The preparation of Co 3 O 4 nanoparticles followed the steps of α- Co ( OH )2 formation through epoxide precipitation reactions, conversion of α- Co ( OH )2 to CoOOH in ammonia regulated alkaline suspension, and transformation of CoOOH to Co 3 O 4 at 100°C. The small size and nonaggregate state of obtained Co 3 O 4 nanoparticles guaranteed the full contact of Co 3 O 4 nanoparticles with electrolyte and the complete penetration of electrolyte into the particles. Consequently, the Co 3 O 4 nanoparticles presented specific capacitance as high as 879.5 F g-1 at scan rate of 5 mV s-1 in 1 KOH . Their specific capacitance remain 82.8% of the initial specific capacitance after 5000 charge and discharge cycles. These results demonstrated that these Co 3 O 4 nanoparticles can be applied as a high performance electrode material for supercapacitor.