Nanostructured materials have attracted much attention because of their unique properties and potential applications in many fields. [1] In the last decade, significant progress in the synthesis of nanostructured materials with controlled size and morphology has been achieved. [2,3] One-, two-, or three-dimensional (1D, 2D, 3D) suprastructures assembled from preformed nanoparticles, [4] nanorods/wires and nanotube arrays, [5] nanostructured hollow spheres, [6] and mesostructured semiconductors have been successfully prepared. [7] In past research, amphiphilic molecules have usually been used either to direct nanoparticle aggregation or to form self-assemblies as templates for the fabrication of inorganic nanostructures. When self-assemblies of amphiphilic molecules are used as templates, the products are structurally and morphologically diverse because of the noncovalent interactions between the template molecules, such as hydrogen bonds, electrostatic interactions, van der Waals forces, and hydrophobic interactions, which lead to diverse inorganic nanostructures. [8][9][10] Using amphiphilic molecule assemblies such as vesicles, [11] microemulsions, [12] micelles, [13] and others [14,15] as templates, a variety of hollow inorganic nanostructures, which are usually spherical, have been prepared. In this paper, cubelike Co 3 O 4 nanoboxes, whose walls are constructed of a single layer of nanocrystals, are introduced. To the best of our knowledge, the only previously observed nanoboxes were constructed of noble metals and alloys, and most recently octahedral Cu 2 O nanocages with single crystalline walls have been generated. [16] Our synthesis is based on surfactant particles formed in alcohol solution and the fabrication of Co 3 O 4 nanoboxes using the separately dispersed cubelike particles as templates, which may provide a simple route to the synthesis of metal oxide nanoboxes. As an important magnetic p-type semiconductor, the spinel Co 3 O 4 has extensive applications in, for example, heterogeneous catalysis, solid-state sensors, electrochromic devices, solar energy absorbers, and as anode materials in Li-ion rechargeable batteries. Nanostructured Co 3 O 4 , including films, tubes, fibers, rods, nanocubes, and nanoaggregates, have been prepared to modify or promote its intrinsic properties.[17] Nanoboxes whose walls are constructed of Co 3 O 4 nanocrystals may have unique and interesting properties. The nanoboxes were obtained after the dispersion of Co(NO 3 ) 2 ·6H 2 O and sodium dodecylbenzenesulfonate (SDBS) in absolute ethanol was heated at 90°C for 8 h and then at 180°C for 3 h, followed by removal of the organics. The X-ray diffraction (XRD) pattern of the product indicates the spinel Co 3 O 4 nature (see Supporting Information, Fig. S1). It is estimated from the transmission electron microscopy (TEM) images that ca. 80% of the products are nanoboxes and the remainder is irregularly aggregated Co 3 O 4 particles. The walls of the nanoboxes are composed of small nanocrystals, and the length of the nanobo...