This study is established with the theory that toughness of ceramics can be improved by reducing the grain sizes of alumina (Al2O3) ceramics. For nano-structured Al2O3 ceramics, nano-sized Al2O3 particles can be synthesized by MOCVD (metal organic chemical vapor deposition) method with Al(CH3)(3). The synthesized particle sizes were 5.6, 11.2 and 22.4 nm, and these particles were used as initial materials. The grain sizes in nano-structured ceramics were controlled by both sintering temperature and holding time. They transformed dramatically from gamma-Al2O3 to alpha-Al2O3 when sintered above 1223 K for two hours. The transformation temperature was lowered by 250 K in comparison the temperature of the phase transformation in bulk. The grain size of nano-structured alumina ceramics grew with increasing sintering temperature. At the sintering temperature of 1173 K, it is necessary of an incubation time for grain growth. The incubation time became longer while particle size decreased. After the incubation time, the rate of grain growth was steeply increased. Above 1273 K, the grain growth directly occurred without any incubation time. (C) 2003 Kluwer Academic Publishers.