Sintering kinetics of the α-Al2O3 powders with average particle size 0.1 μm and ca.1% ZrO2 impurity was investigated. Several two-step sintering methods were tried, and the results were compared with the conventional (one-step) process. The temperature (<1600oC), holding time (up to 20 h), heating rate (2 oC /min to 90 oC/min), initial grain size, and porosity were controlled. The optimal results of two-step sintering, a smaller grain size (0.57 μm) and a good density (>98% TD) were achieved by heating to 1450oC, then holding at 1350oC for 20 h. The sintering mechanism was determined, belonging to lattice diffusion in the temperature region of 1400 to 1600oC. The activation energy was 688 kJ/mol, which was interpreted as a volume diffusion of Al3+ ions in polycrystalline matrix.