Raman spectroscopy has been applied to investigate in-situ the phase transition of a LBO (LiB₃O₅) crystal near its melting point in order to explain the discrepancies between the experimental results observed in the LBO crystal growth process and the predicted results obtained from the Li₂O–B₂O₃ phase diagram. When the LBO crystal begins to melt, it first decomposes to the kinetic products Li₂B₄O₇ and B₂O₃; then the Li₂B₄O₇ reacts with the undecomposed LBO to form the thermodynamic product Li₃B₇O₁₂. On the basis of these results, a set of models have been proposed to describe the structural transformations present in the phase transition. Additionally, our experimental result indicates that Li₃B₇O₁₂is stable/metastable at room temperature. Its Raman spectrum has been calculated by the density functional theory method for identification of the Li₃B₇O₁₂ crystalline phase in a mixture. The result shows that Li₃B₇O₁₂ has three strong characteristic Raman peaks located around 595, 775 and 1040 cm^？1.