The synthesis of calcium hexaboride (CaB6) powder via the reaction of calcium carbonate (CaCO3) with boron carbide (B4C) and carbon has been investigated systematically in the present study. The influences of heating temperature and holding time on the reaction products have been studied using X-ray diffractometry, and the morphologies of CaB6 obtained at various temperatures and holding times have been investigated via scanning electron microscopy. The interaction in the CaCO3-B4C- carbon system by which CaB6 is formed is a solid-phase process that passes through the transition phases Ca3B2O6 and CaB2C2. The optimal conditions for CaB6 synthesis are a holding time of 2.5 h at a temperature of 1673 K, under vacuum (a pressure of 10(-2) Pa). CaB6 powder has the same morphology as B4C, and the properties and the shape of CaB6 powders can be improved by choosing good-quality raw materials.