Nearly monodisperse Co3O4 nanospheres were fabricated via a facile polyethylene glycol 400-mediated solventhermal route followed by a calcination process at 500 °C. The structure, morphology, and properties of the products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry, and UV–vis spectrometry. The results showed that the products were Co3O4 nanospheres of 160–170 nm in diameter and were composed of nanoparticles of ca. 40 nm. The possible formation mechanism was discussed on the basis of experimental results. Furthermore, optical property of the products was characterized.