Three-dimensional hierarchical Co3O4 structures with high densities of secondary Co3O4 nanowires grown on primary Co3O4 fibers have been fabricated employing a coprecipitation growth on an electrospinning PVA/cobalt acetate nanofiber template followed by annealing in air. The structural analyses showed that as-prepared amorphous CoC2O4 nanowires converted into crystalline spinel Co3O4 after annealing. The morphology of the hierarchical Co3O4 structures could be further controlled by adjusting the mixing ratio of H2C2O4 to CH3CH2OH.