Dense B4C matrix composites were synthesized by spark plasma sintering (SPS) process using CeO2 powders as the sintering aid. The effects of CeO2 on densification and properties of B4C were studied, and compared those with sample without additive. X-ray diffraction and transmission electron microscopy was employed to examine the phase and microstructure of the composites respectively. The results indicate that the addition of CeO2 powder can significantly improve the sintering propertyof B4C. The relative density of samples increased because of the existence of generated CeB6 between B4C grains. CeO2 content ranged from 1 wt.% to 8 wt.%. The specimen with 4 wt.% CeO2 sintered at 1750℃under a pressure of 35 MPa exhibited relative density of 96.7% and Rockwell hardness of 90.7HRA. Key words: boron carbide; cerium hexaboride; ceriumoxide; SPS; densification