An unprecedentedly facile, cheap, green, and scalable approach to fabricate cobalt oxide nanoparticles has been developed in this work. By directly annealing cobalt acetate tetrahydrate, Co3O4 with a trace amount of CoO was formed at 300 degrees C in air. A rapid morphological change (<30 min) from chunk to nanoparticles is elucidated. When applied as the anode material for lithium-ion batteries (LIBs), they demonstrated an excellent lithium storage capability of 1150 mAh/g at a current density of 0.2 A/g over 100 cycles and a superb rate capability as high as 820 mAh/g at 4 A/g. This approach with low labor and energy cost shed light on a new route for the industrial production of cobalt oxides, opening more opportunities for their applications in electrochemical devices.