Regular features of variation of the structure, phase composition and hardness characteristics in a β-phase-based titanium alloy Ti - 10V - 2Fe - 3Al subjected to isothermal treatment in a melt of lead and tin for 5 sec - 32 h at 250 - 800 °C from the temperature of 860 °C of heating in the β-range are considered. The types of the phases precipitated in the process of isothermal decomposition of the high-temperature β-solid solution and the dependences of the lattice constant of the β-phase and of the hardness on the temperature-and-time mode of the treatment are determined. A diagram of isothermal decomposition of the β-solid solution in alloy Ti - 10V - 2Fe - 3Al is plotted.