A novel petal-like cobalt oxide (PCO) structure has been fabricated by electrodeposition of the nanostructured Co film followed by elevated-temperature oxidation. The structure exhibits monodisperse petal-like cobalt oxide nanosheets and core-shell structure with oxide as shell and metal as core. The morphology was studied by changing the surface structure of the initial Co film and oxidation temperature, finding that the PCO could only be obtained by calcining the arched Co film at 500 degrees C. The growth mechanism is briefly discussed based on the Caberra-Mott theory. The electrochemical behaviour analysis indicates the prepared material's potential as electrode materials in supercapacitors.