Fatigue fracture properties of hot isostatic pressed WC-12%Cc alloys having coarse and fine WC particles were investigated and macro-and microfractografic analyses were carried out. The results obtained are as follows: (1) Fatigue strength increases with increase of WC particle size. (2) Fatigue strength of hot isostatic pressed alloy becomes larger than those of conventionally sintered alloy. (3) Fractographic analysis reveals the existence of characteristic fracture surface of fatigue. A some region of fatigue fracture surface looks weakly bright. In this region, saw tooth type crack can be observed. These pattern consist from the Co (h.c.p.) phase.