Effects of 1 mass% of each of ZrC, VC, MO2C, Cr3C2, and TaC addition on micro structure, high and room temperature Vickers hardness, and transverse rupture strength of submicron WC-8mass%Co hardmetal were investigated.Results obtained were summarized as follows: Grain growth of mean grain size of WC was inhibited, and the mechanical properties of submicron hardmetals were improved by the addition of each carbide.This raising of hardness was seemed to be governed by refinement of WC grains by the carbide addition. Vickers hardness of submicron hardmetals with carbide additions, at elevated temperature, are higher than that of these hardmetals without carbide addition. There are two different ranges of temperature dependence on hardness of submicron hardmetals. In this paper, the point of refraction is defined as temperature. The softening temperature was higher in the order of no addition, VC, TaC, ZrC, MO2C, and Cr3C2 addition.This reason has been estimated to be solid solution strengthening of cobalt binder phase.