Abstract: The mechanical properties,reinforcement and fracture mechanism of the composites fabricated by in situ reaction method in the Al-TiO2-C system were studied.When the C/TiO2 mole ratio was zero,the reinforcements of the composites were composed of α-Al2O3 and Al3Ti,the ultimate tensile strength and elongation were 274MPa and 3.0% respectively at room temperature.The fracture mechanism of the composite was characterized by initiation firstly in Al3Ti rods and then propagation to the interface.When the C/TiO2 mole ratios increased,the amount of Al3Ti phase decreased,the ultimate tensile strength and elongation increased.When the C/TiO2 mole ratio reached 1,the Al3Ti phase was almost eliminated,the ultimate tensile strength and elongation were promoted to 351 MPa and 6.0% respectively.There were big ductile dimples around the Al3Ti and fracture by themselves in the fracture surfaces of the composites.The fission first occurred in the Al3Ti and then diffused to the matrix.Therefore,the Al3Ti phase was not benefit to strengthening the composites.