A series of activated Al-Co3O4 powders were prepared by high-energy ball milling, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and differential scanning calorimeter (DSC). The properties of these activated Al-Co3O4 powders reacting with the water steam were systematically investigated at 700 degrees C, 800 degrees C, and 900 degrees C. Morphologies and phases of their reaction products with water steam were characterized by SEM, XRD, and the residual metal aluminum content in products was also measured. The results showed that the reaction properties of the Al-Co3O4 powders with the water steam were closely related to the milling time. The Al-Co3O4 powder experiencing 3h milling showed the finer particle size, lower initial oxidation temperature, earlier autoignition, and longer combustion in the water steam at high temperature than the other samples. The Co2Al9 alloy was detected in the reaction products of Al-Co3O4 powders with water steam. The investigation demonstrated that the activated Al-based powders could be prepared with the Al and Co3O4 through high-energy milling process.