The as-prepared cobalt oxide (assigned as CoO x ) was fabricated by precipitation–oxidation from aqueous cobalt nitrate solution using sodium hydroxide and oxidation with hydrogen peroxide. Another series of pure cobalt oxides was refined by the decomposition of CoO x in a nitrogen environment at temperatures of 280, 450 and 950°C (D-280, D-450 and D-950, respectively). Phase transformation, structural properties and red-ox properties were characterized by thermogravimetry-mass spectrometry (TG-MS), X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy and temperature-programmed decomposition/reduction (TPD/TPR). Analysis of the thermal behavior on CoO x revealed that a series of pure cobalt oxide with particle sizes of 10–20nm could be obtained easily. The results demonstrated that the refined samples D-280, D-450 and D-950 were CoO(OH), Co3O4 and CoO, respectively.