Ultrafine-grained W-5wt.% Cr-5wt.% Y (W5C5Y) alloy was prepared by the spark plasma sintering method. Investigation of the microstructure showed that the grain growth was suppressed by the addition of Cr and Y. They not only enhance the density of sintered materials, but also purify and strengthen the grain boundaries through the second-phase particles formed by the reaction with free O. Ultrafine-grained W5C5Y exhibits ultrahigh hardness, which is much higher than that of ITER-grade W. It also shows high thermal stability even at the annealing temperatures of 1000 °C and 1100 °C, and exhibits higher irradiation resistance compared with ITER-grade W.