(Ti,Mo)Al/Al2O3 composites were successfully synthesized utilizing in situ reactive hot pressing method with Ti, Al, and MoO3 powders as starting materials. A possible synthesis mechanism was proposed to explain the formation of (Ti,Mo)Al/Al2O3 composites. The investigation results indicate a probable reaction process that molten Al reacted with MoO3 to form Al2O3 and Mo, and the TiAl matrix grains were refined increasingly by Al2O3 with the addition of MoO3 increased, accompanying with a small quantity of Mo containing phase AlMoTi2 formed in the fabricated composites. Meanwhile, the microstructure and mechanical properties of the (Ti,Mo)Al/Al2O3 composites were characterized. The as-synthesized composites exhibited lamellar structure of TiAl intermetallic compound and the in situ formed fine Al2O3 particles dispersed at the stratified TiAl matrix grain boundaries hindering the growth of the grain size of the matrix. And the Rockwell hardness, flexural strength, and fracture toughness of the as-prepared (Ti,Mo)Al/Al2O3 composite were 44.08 HRC, 684 MPa, 7.63 MPa·m1/2, which improved by 57.4%, 107.3%, and 38.7% compared to monolithic TiAl, respectively. The reinforcing mechanism of the material was also discussed.