ZrB2 powders with different particle size or different morphologies have been synthesized by boro/carbothermal reduction (BCTR) method using ZrO2, B4C and graphite or carbon black as starting materials in this work. Results revealed that the carbon black with fine particles decreased the synthesis temperature and resulted in a finer ZrB2 powder compared with graphite in vacuum. However, the synthesis temperature was almost the same for both the carbon black and graphite cases if the reaction took place in argon atmosphere. Furthermore, vacuum atmosphere led to the formation of rod-like ZrB2 powder, whereas argon atmosphere resulted in quasi-spherical ZrB2 powder. Thermodynamic calculation was conducted and possible mechanisms were discussed for understanding the above phenomena. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.