Two calcium-doped alpha-SiAlON compositions (Ca0.6Si10.2Al1.8-O0.6N15.4 and Ca1.8S6.6Al5.4O1.8N14.2) were prepared by hot pressing at 1600degrees and 1500degreesC, respectively, for complete phase transformation from alpha-Si3N4 to alpha-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of alpha-SiAlON. Elongated ot-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the alpha-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the alpha-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development.