Boron and lithium play an important role in many industries, which are widely distributed in brines of the Qaidam basin. In order to effectively separate lithium and boron mixed salts, the experimental solubilities, solution densities, and refractive indices of the quaternary system (Li + Na + Cl + BO2 + H2O) at T = 288.15 K and P = 0.1 MPa were measured. There are six minerals, corresponding to NaCl, LiCl center dot 2H(2)O, NaBO2 center dot 4H(2)O, LiBO2 center dot 8H(2)O, LiBO2 center dot 2H(2)O, and the double salt NaCl-NaBO2 center dot 2H(2)O, that existed in this system. LiBO2 center dot 8H(2)O occupies the greatest part of the phase region, while LiCl2 center dot H2O covers the smallest. These results show that LiBO2 center dot 8H(2)O could be easily crystallized and separated from this system. LiBO2 center dot 8H(2)O will dehydrate and transform into LiBO2 center dot 2H(2)O in the concentrated LiCl aqueous solution.