[en] Microstructure and some properties of two sections of the ternary Nb-Ti-O system have been studied in that part of the system where there is no separation observed of liquid phases with a formation of two immiscible layers. It has been shown that at an O concentration of 5 at.% the section paralled to the side Nb-Ti is similar to the binary Nb-Ti system in the character of phase equilibrium, but the zone α+β is enlarged while the one-phase zone (based on the β-phase) is narrowed. As a result of this, the transformation +b reversible α begins at higher concentrations of Nb compared to Nb-Ti alloys. The section Nb-TiO₃ of Nb-Ti-O system is quasibinary which allows a triangulation to be made of the Nb-Ti-O system with isolation of two systems: Nb-Ti-Ti₃O and Ti₃O-Nb-O. The character of the phase equilibrium between Nb and Ti₃O is described by a phase diagram of the eutectic type