Sphere-like shaped cobalt oxide nanoparticles (Co3O4) were synthesized by a simple wet chemical method using cobalt chloride as precursor and cetyl trimethylammonium bromide (CTAB) as surfactant. Their structural and surface morphologial properties were characterized by high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). XRD measurement exhibited the structure of Co3O4 nanocrystals for annealed samples. The TEM results showed the sphere-like shaped cobalt oxide nanoparticles with good uniformity in the presence of CTAB surfactant. The SEM images revealed that the particles changed to spherical shape and the size of cobalt oxide nanoparicles increased in the range of 25-45 nm with increasing annealing temperature.