Abstract: The combined sintering process (vacuum sintering plus HIP sintering) was introduced for producing ultrafine grained WC Co cemented carbides. The shrinkage and densification of the compacts during the combined sintering were studied. The results show that, the high selfdiffusion activities of W and C atoms enable them to quickly dissolve into the cobalt phase, for which the local liquid sintering takes place beforehand. The local liquid sintering is intimately correlated with the rapid shrinkage of the compacts and the substantial WC grain growth during the vacuum sintering stage (i.e.solid state sintering stage).