The impact fatigue performances of different combinations of WC grain size and Co phase cemented carbides were tested by low cycle impact test procedure, and then, their toughness and toughening effects were evaluated. The results have shown that the low cycle impact fatigue performances of cemented carbides are enhanced with the increase of cobalt content when the WC grain size is certain.The impact fatigue resistance of cemented carbide with an average grain size of 1.8 μm is weaker than cemented carbide with an average grain size of 6.5 μm at the same level of cobalt content. The low cycle impact fatigue performance is more effective than the conventional toughness indicators of cemented carbides in evaluating toughness and toughening effects.