The selenite of tantalum was precipitated quantitatively from sulfuric-nitric-tartaricoxalic acid solution by means of selenous acid.After digesting on water bath, the precipitate was filtered, washed with dilute nitric acid containing selenous acid and finally with 95% ethanol.The fresh precipitate is completely soluble in a solution of hydrochloric and oxalic acids or the latter alone.The selenous acid in the solution thus obrained was titrated with standard thiosulfate solution.Based on the experimental results, the molar ratio of Ta, O5:Se02 in the precipitate is found to be 1:1.