The detailed microstructure characteristics and the formation regulation of the duplex microstructure of Ti-23Al-17Nb (at%) alloys under different heat treatment conditions were studied. The effects of detailed microstructure characteristics on the mechanical properties of alloys were also investigated. The approaches to improve the both tensile and endurance properties at elevated temperature were discussed. The results indicate that for the alloys forged in (α2+B2) phase field, the duplex microstructure can be obtained either by treatment of solution in (α2+B2) field and oil quenching plus aging in (α2+B2+O) field. The volume fraction, size and distribution pattern of O phase laths can be controlled well. The relatively lower aging temperature is of benefit to form the finer and more random distribution of O phase laths. Increasing the volume fractions of O phase laths can improve the endurance properties at elevated temperature but decrease the room-temperature elongation in the case of similar sizes and same percent content (15%-20%) as equiaxed α2 particles, while the finer sizes of O phase laths can increase the tensile properties both at room and elevated temperatures, but decrease the endurance properties. The optimum matching of tensile strength, elongation and endurance properties of the alloys at elevated temperature can be obtained by the heat treatment of 1060 oC solution and oil quenching plus 850 oC aging