Even if cemented carbide results very strong due to its composition its real strength is not reached in practice since the presence of defects in the structure or at the surface that increase the local stress concentration during the application of a stress. Indeed the fracture load is not only a function of the intrinsic strength of the WC-Co which depends on the chemical composition and microstructural properties of the material but especially depends on the presence of defects into the part. In this work the mechanical properties such as hardness fracture toughness and transversal rupture strength (TRS) of differently WC-Co grades were investigated. The TRS was measured by means of the three-point bend test. Due to the wide scatter of TRS values the obtained results were analyzed within the Weibull theory. The grade with the intermediate Co concentration presents a bi-modal Weibull distribution with lower characteristic strengths compared to the grade with the lower Co amount. In order to justify this behaviour the correlation between the mechanical properties and the chemical composition and microstructural parameters were evaluated and the microporosity and the fracture surfaces of the different grades were investigated.