Fatigue strength and fracture mechanism of a medium carbon steel with HVOF thermally sprayed WC-Co coatings were investigated under rotating bending. Two types of commercially available WC-Co powders were used, which have similar total chemical composition with different manufacturing processes. The fatigue strengths of the specimens with thick coatings were lower than that with thinner ones. Especially, it was found that the fatigue strengths of the thick coating specimens decreased more greatly than that of the grit blasted ones. Also, the morphology of the fatigue crack depended on the type of powders and the thickness of the coating. Futher more, an embedded Al2O3 grit and a crack generated during the grit blasting were found near the fatigue fracture origin of the coated substrate.