beta-Ti alloys are promising candidates for biomedical applications due to their high strength, high corrosion and wear resistance, and low elastic modulus. This study focuses on phase evolution in a low modulus Ti-35Nb-7Zr-5Ta (TNZT) alloy, systematically examined via isochronal and isothermal annealing, and its influence on microhardness. The observations indicate that the highest microhardness value was achieved at an aging temperature of 400 A degrees C. The microstructural evolution at this temperature was investigated via systematic isothermal annealing treatments, and the results indicate a progressive transformation from beta + omega + O' (solution treated and quenched) to beta + omega + alpha (after isothermal annealing at 400 A degrees C/6 h), with the dissolution of the metastable orthorhombic O' phase and the formation of the stable alpha phase. The maximum hardness corresponded to a highly refined mixture of co-existing omega and alpha phases after prolonged annealing for 48 h at 400 A degrees C. The coexistence of both omega and alpha phases after such prolonged annealing indicates that at 400 A degrees C, omega is in metastable equilibrium, despite the concurrent precipitation of the equilibrium alpha phase.