Using aluminum powder with average particle size of 22.1 $mu$m, aluminum compact made by Pressureless Powder Packing Method showed 52% green density. The activation energy of aluminum oxidation was cal-culated from the weight change of TG, and it was varied in the range of 16~64 kJ/mol. It was found from the variation of the activation energy and the observation of the microstructure that oxidation was de-pendent on the destruction of oxide film and the melt-out of aluminum. Aluminum compact was reaction-bonded at 1000~140$0^{circ}C$ for 4~60hrs, and oxidation was dependent on temperature rather than time. Reac-tion-bonded aluminum oxide at 140$0^{circ}C$ for 60hrs showed 92% oxidation percent. It was sintered at 1$600^{circ}C$ for 15hrs and the sintered body showed 62% relative density.