<p>The phase equilibria of La-Fe-B alloys at 873&#xa0;K were studied by means of the equilibrated alloy method using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and x-ray diffraction (XRD). It was confirmed that the ternary intermetallic compound La₂Fe₁₄B (τ₁) with the Nd₂Fe₁₄B-type structure and space group <i>P</i>4₂<i>/mnm</i> is not stable at 873&#xa0;K, while the ternary intermetallic compound La_1.1Fe₄B₄ (τ₂) with the Nd_l+εFe₄B₄-type structure and space group <i>Pccn</i> exists. The isothermal section of the La-Fe-B ternary system at 873&#xa0;K was determined. Based on the experimental results determined in this work and reported in the literature, thermodynamic calculation of the La-Fe-B ternary system was conducted using the CALPHAD method in combination with the previous assessments of the La-Fe, Fe-B and La-B binary systems. The calculated results including isothermal sections, vertical sections and liquids projection are in good agreement with the experimental results. A set of self-consistent thermodynamic parameters of the La-Fe-B ternary system was finally obtained, which is a good basis of the devolvement of a thermodynamic database of Nd-La-Fe-B alloys to explore Nd-Fe-B permanent magnets with high-performance and low-cost.</p>