Calciothermic reductions of Ta 2 O 5 and Nb 2 O 5 are proposed aiming at the fine powder preparation for the larger capacitance of condensers. Because the molten CaCl 2 can coexist stably with metallic Ca, and because it can dissolve a few mol%Ca and about 20mol%CaO, the reductant Ca can be supplied to the oxide via molten CaCl 2 , and the reaction by-product CaO can be in situ eliminated from the reaction interface. The metallic powder was obtained after an hour at 1173K. In the prolonged time the particles sintered together, but oxygen was gradually removed to the level of a few thousands ppm.