Through melting, refractory metals and alloys are becoming important for use as structural materials. Vacuum-melting is considered to be able to provide high-purity ingots because of its purifying effect, particularly the effect of evaporation deoxidation via volatile oxides. Thermodynamic calculation leads us to predict a limited possibility for deoxidizing Ti, Zr, Hf, a good possibility for Mo and W, and an intermediate possibility for V, Nb, and Ta. The sponges of these metals containing oxygen were degassed under high vacuum at temperatures below or over the melting point, and the change in oxygen content was measured as a function of time. The observed rates of purification agreed well with the thermodynamically estimated deoxidizing tendencies. Kinetic analysis of the degassing curves obtained for the Nb-O, Ta-O, Mo-O, and W-0 alloys showed that the rate-determining step was the diffusion of oxygen in the metal or the recombination of oxygen with the base metal atoms and the transfer of the molecules into the vacuum. If carbon was present in the metal, the oxygen liberation was considerably accelerated. However, an excess of oxygen to carbon was necessary for the carbon level to be sufficiently lowered at the same time.