Uniform Co spherical assemblies were prepared via a facile hydrothermal reduction approach in the presence of surfatctants with a yield of 98%. The assembled nanostructures were composed of ordered nanoplatelets with a thickness of similar to 20 nm, as characterized by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), and high-resolution TEM (HRTEM). This material exhibits ferromagnetic characteristics and has a high surface area, showing potential applications for catalysts and other related nanodevices.