© 2022 Elsevier LtdSquare-shaped monolithic B4C and B4C-ZrB2 composites were produced by spark plasma sintering (SPS) method to investigate the effect of 5, 10, 15 vol% ZrB2 addition on the densification, mechanical and microstructural properties of boron carbide. The relative density of B4C increased with the increasing volume fraction of ZrB2 and density differences in different regions of the sample narrowed down. Homogeneous density distribution and microstructure were accomplished with the increasing holding time from 7 to 20 min for the B4C-15 vol% ZrB2 composites, and the highest overall relative density was achieved as 99.23%. The hardness and fracture toughness of composites were enhanced with the addition of ZrB2 compared to monolithic B4C. The enhancement in fracture toughness was observed due to the crack deflection, crack bridging and crack branching mechanisms. The B4C-15 vol% ZrB2 composite exhibited the combination of superior properties (hardness of 33.08 GPa, Vickers indentation fracture toughness of 3.82 MPa.m1/2).