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[References: 12 tit.]

The paper presents the experimental data observed in the microstructure and phase composition of ultrafinegrained Ti-40 mass % Nb (Ti40Nb) alloy after high-temperature annealings. The ultrafine-grained Ti40Nb alloy is produced by severe plastic deformation (SPD). This method includes multiple аbс-pressing and multi-pass rolling followed by further pre-recrystallizing annealing which, in its turn, enhances the formation of ultrafine-grained structures with mean size of 0.28 [mu]m involving stable [beta]- and [alpha]-phase and metastable nanosized ω-phase in the alloy. It is shown that annealing at 500°С preserves the ultrafine-grained structure and phase composition. In cases of annealing at 800°С the ultrafine-grained state transforms into the coarse-grained state. The stable [beta]-phase and the nanosized metastable [phi]- phase have been identified in the coarse-grained structure.