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WC powders with different particle sizes and ultrafine Co powders were mixed to form the initial powders. Afterwards ultrafine WC-Co cermet bulks were prepared by direct SPS and a new method combining vacuum pretreatment with SPS. Results show that the samples prepared by pretreatment and SPS have a little lower hardness but higher fracture toughness and much higher tensile strength than those by direct SPS. The analyses of microstructures and properties indicate that the vacuum pretreatment has important effect on the WC-Co cermets by SPS. It can release the adsorbed gas, cancel the “Co lake” and obtain completely densified bulks without significant grain growth.