Abstract Alumina hydrates were prepared by the wet chemical method under different pH values and subsequently calcined through both conventional and microwave heating approaches. After calcination at 500 °C for 2 h, amorphous precursor was partially transformed to α-alumina. NH₄NO₃ remaining in the dried precursor without further washing after precipitation reaction was found to increase the transformation temperature, which is different from previous published results. Microwave calcination was also employed and can dramatically enhance the phase transformation rate in comparison with the conventional method. A combination of microwave heating and amorphous precursor may be a viable strategy to fabricate α-alumina at low temperatures rapidly.