Abstract The fracture toughness of WCCo alloys has been determined on single-edge notched beam (SENB) specimens precracked by electron discharge machining (EDM). The results agree satisfactorily with the fracture toughness measured by Lueth on double cantilever beam specimens of the same material. The crack geometry of the SENB specimens with EDM notch is compatible with the requirements of linear elastic fracture mechanics. The results show a linear correlation between GIC and σyλ, where σy is the in-situ yield strength of the binder phase and λ is the mean free path. The variation of fracture toughness as a function of yield strength and mean free path of the binder phase, and the fracture modes observed by fractography are comparable with the Rice and Johnson criterion for crack extension controlled by ductile fracture.