The effect of the oxygen content and the annealing temperature on the tensile behavior of the Ti-1.5Al-3Fe-0.25Si-(0.1~0.5)O alloy was investigated. The tensile properties were dependent on the volume fraction of the microstructure constituents, i.e. the equixed α, equixed β and lamellar α. The results showed that the O-partitioned equixed α had a much higher strength compared to the equixed β. The strength of the lamellar α increased with increasing the annealing temperature because the O content of the lamellar α increased. Ti-1.5Al-3Fe-0.25Si-0.3O alloy annealed to 900 o C where the volume fraction of lamellar α was the highest exhibited an excellent combination of the strength (1198.5 MPa) and ductility (27.5%). The effect of the lamellar α on the ductility was discussed.