Carbothermal reduction-nitridation (CRN) of SiO2, is an attractive method to manufacture Si3N4 powders with controlled grain morphology, Moreover, beta-SiAlON powders could also be synthesized from either pure powder mixture or some inexpensive raw minerals by CRN and the resulting powders favored the sintering of SiAlON product. However, there have been few works on preparing alpha-SiAlON powders so far. In this work, Ca alpha-SiAlON powder was synthesized by CRN: of a SiO2-Al2O3-CaCO3 mixture. An unusual morphology of hollow beads 200 to 500 nm in diameter with a great deal of nanosize alpha-SiAlON particles around 10 to 30 nm in diameter was observed from the resultant Ca alpha-SiAlON powders, which has not been reported for SiAlON ceramics before.