The influence of oxygen concentration and the phase composition on various properties of Ti–42Al–5Mn (at%) forged alloy was evaluated, with the objective of expanding the utilization of this material. As a result, it was established that reduced oxygen concentration and increased β-phase fraction are effective for increased manufacturability (hot forgeability and machinability), and that increased oxygen concentration, reduced β-phase fraction, and increased lamellar structure fraction are effective for increased high-temperature strength. Accordingly, it is difficult to achieve optimization of all characteristics simultaneously. Nevertheless, at a high oxygen concentration of 0.16wt% obtained via ceramic crucible melting, relatively favorable levels of all properties can exist simultaneously.