Abstract: Boric acid and sodium nitrate were prepared by the leaching of Tibet borax mine with boric acid mother liquor and by the subsequent acidification of the borax solution.By controlling the concentration of the reactants and other related process conditions，the crystallization of boric acid and sodium nitrate can be realized simultaneously.By using the property of difference in relative densities，boric acid and sodium nitrate were isolated with gravity separation.Results showed that the yields of boron and sodium were 92.0% and 91.5%，respectively.The product quality conformed to the state standards.Additionally，boric acid mother liquor did not need to be evaporated during the process.

Key words: nitric acid, borax mine, boric acid, sodium nitrate