Abstract: Ultra-fine ZrB2/SiC composite ceramic powders were synthesized at temperatures from 1 300 ℃ to 1 700 ℃ by carbothermal reduction using zirconium dioxide, boric acid, silica sol and carbon black as raw materials. The influences of synthesis temperature and reactant ratio on the phase composition, micro morphology and particle size of the composite powders were investigated by XRD and SEM. The results show that the completeness of carbothermal reduction for the synthesis of high purity ZrB2/SiC composite powders was needed of over dosage of boric acid (molar ratio of ZrO2 and B2O3 was 1∶1.5) when synthesized at 1 650 ℃ for 1 h. The composite powders had an average particle size of 0.4 μm, and different particle shapes after prepared at different temperatures. With the increase of synthesis temperature, the whisker and rod particles gradually reduced while ball particles increased.