In this work, spinel-type Co3O4 spherical nanoparticles were easily prepared via decomposition of the hexamminecobalt(III) nitrate complex, [Co(NH3)(6)](NO3)(3), at low temperature (200 degrees C). The product was characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) specific surface area measurement and magnetic measurements. The results confirmed that pure single-phase Co3O4 nanoparticles with weak ferromagnetic behavior were obtained by this method. TEM images showed that the Co3O4 nanoparticles are sphere-like with an average diameter size of around 15 nm. The optical spectrum indicated two direct band gaps at 2.15 and 3.56 eV which are blue-shifted relative to reported values for the bulk sample. Using this fast and simple method, Co3O4 nanoparticles can be produced without expensive and toxic solvents or complicated equipment. (C) 2012 Elsevier Ltd. All rights reserved.