Liquid-solid phase equilibria are studied in the eutectic benzoic acid-naphthalene system by means of thermic analysis (DTA, CTA), on the basis of which the liquidus line and eutectic point (xe ≈ 50 mol %, Te ± 340 K) are determined and the phase diagram is constructed. Average precrystallization supercooling temperatures ΔTL− of the liquid phase relative to liquidus temperature TL are determined, allowing us to locate the region of solution metastability on the phase diagram. Excessive functions of the components in the liquid phase are found via thermodynamic modeling using the Margules equation and experimental data. The boundaries of the region of liquid solution metastability are estimated from the thermodynamic conditions of solution stability.