Superplastic behavior and cavitation were investigated for WC-15 mass % Co cemented carbides with the WC grain sizes of 0.7 mu m (A) and 5.2 mu m (B), WC- 10 mass % Co cemented carbide with the WC grain size of 1.5 mu m (C) and WC-5 mass % Co cemented carbides with the WC grain sizes of 0.5 mu m (D) and 2.5 mu m (E) by tensile tests at 1473 K. WC contiguity were 0.51, 0.31, 0.27, 0.56 and 0.49, respectively. The large elongations about 200 % were obtained for the B and the C having smaller values of WC contiguity compared to the other cemented carbides. The values of cavity volume fraction for them were less for the other cemented carbides, furthermore, cavities formed at WC/WC interfaces. Therefore, it is noted that the distribution of the Co phase is important for superplasticity of the cemented carbides.