Controlling the morphology of nanostructured manganese oxide materials can be an effective way to improve capacitance for supercapacitor applications. Herein we demonstrated for the first time the synthesis of MnO/Mn3O4 nanocomposite tetrahedrons with a porous structure, and a new method to synthesize porous urchin-shaped MnO/Mn3O4 nanocomposite. Compared with the non-porous MnO nanocrystalline octahedrons and the mixture of non-porous MnO and Mn3O4, the porous MnO/Mn3O4 nanocomposite ‘urchins’ exhibited superior capacitance in supercapacitor application, while the porous MnO/Mn3O4 nanocomposite tetrahedrons displayed superior stability. The excellent capacitance and stability of these nanocomposites could be explained in terms of the much higher surface area associated with their porous structure. These porous nanostructures offered a good model to investigate the effects of morphology and surface area on the capacitance of nanocomposites.