The authors employ methods of spontaneous crystallization on a platinum loop, modified visual polythermal analysis (VPA), solid phase synthesis, differential thermal analysis (DTA), X-ray powder diffraction (XRD) analysis and chemical analyses, in order to study chemical processes and phase formation in the BaB2O4–LiF–Li2O system. In this system the fields of primary crystallization of β-BaB2O4 are determined. The primary crystallization field of the low-temperature barium borate phase for the BaB2O4–LiF–Li2O system is proved to lie in the range 72–60 mol% BaB2O4. A series of experiments have been carried out on the growth of bulk barium borate crystals in this system.