Metastable beta-Ti alloy are typically known to precipitate additional phases (alpha and omega phases) during thermal treatment. The morphology, size and distribution of these precipitates determine in large part the mechanical properties of the alloy. In this communication, recent results on the beta-phase decomposition from the as-quenched Ti-6.8Mo-4.5Fe-1.5Al composition induced by heat treatment are presented. By using appropriate thermal treatments, the precipitation of nanostructured omega and alpha phases was observed and characterized by resistivity measurements and high-resolution transmission electron microscopy (HREM). The different stages of the precipitation have been investigated in order to understand the nanocrystallization mechanism. Athermal metastable omega(ath) particles were observed in the as-quenched beta-Ti matrix, due to a diffusionless mechanism (martensitic transformation) occurring during quenching. After heating, the diffusion-controlled process has led to the formation of omega(iso) ellipsoidal nanoparticles distributed through the beta-Ti matrix. In this study, a particular attention has been made on the precipitation conditions and on the morphology control of these omega(iso) nanophases. The direct interest of such a knowledge is crucial because the omega(iso) precipitates is shown to behave as nucleation site of an extremely fine and dispersed cc phase leading to higher mechanical properties of the final stable nanostructured (beta+alpha) duplex alloy.