WC–ZrO 2 (3Y) composites were densified by spark plasma sintering. The influence of ZrO 2 content on the densification behavior, microstructure and mechanical properties of the composites were investigated. Adding ZrO 2 into WC can facilitate sintering, but will not cause rapid WC-grain-growth. After sintering, most of the tetragonal ZrO 2 remain until at room temperature, and partially transform to monoclinic structure during fracture, which exerts toughening effect. The Palmqvist cracks, rather than half-penny cracks, are observed in the high ZrO 2 -content grade composites (⩾6wt.%). As the ZrO 2 content increases from 0 to 6wt.%, the fracture toughness of the WC materials increases from ∼6MPam 1/2 to ∼10.6MPam 1/2 with an elevation of ∼77%; while the ZrO 2 content continues to increase to 10wt.%, the fracture toughness of the WC–ZrO 2 composites is near constant.