In this report the liquid-liquid solvent extraction and the separation of Ta and Nb have been studied, using tributyl phosphate (TBP) as an organic solvent and hydrofluoric acid solution as an aqueous solution. The extractability of a fluoride complex of Ta and Nb from HF solution into TBP was found to be a function of HF acidity, TBP concentration , oxide concetration, volume ratio of organic solvent to aqueous solution, and number of extraction operation . The results obtained can be summarized as follows: (1) The Ta percentage extractions and the Ta distribution ratio decreased with an increase in HF acidity at a constant TBP concentration, but decreased with a decrease in TBP concentration at a constant HF acidity. The percentage extractions of Nb and Nb distribution ratio rose with a rise in HF acidity and TBP concentration. (2) The separation factor augmented with diminishing HF acidity, especially under 3 N HF. (3) Both percentage extractions of Ta and Nb decreased inversely with the rising oxide concentration in aqueous solution. (4) The increase in the volume ratio and frequency of extraction increased both percentage extractions of Ta and Nb. (5) The organic extract ertracted with TBP included little impurity. (6) The HF-TBP system had larger extractability of Ta and Nb , particularly in low HF acidity, better separation factor and higher purity of the organic extract than the HF-hexone system.