Nd-doped α-SiAlON starting composition (Nd0.33Si9.38Al2.62O1.62N14.38) was prepared by gas pressure sintering at 1825°C for 3 hrs. In order to explore the effect of post heat treatment on the developments of elongated α-SiAlON grains, sample was heat treated at 1800°C for 4-12 hrs. It was found that post heat treatments promoted formation of the elongated α-SiAlON grains. The controlling mechanism of grain growth was determined via plotting on a graph the growth in width/length versus time graphics using Image Analysis method. Different growth rates were found between the length and width direction of the α-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development.