The Al_2O_3 ceramics was bonded with Ti-6Al-4V using (Ag_ 72Cu_ 28)_ 97Ti_3 as filler metal under the conditions of 1 073 k~1 173 K and 18 ks. The interface structure and formation mechanism of joints were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). It was found that the interface structure of diffusion-bonded joints is Al_2O_3/Cu_2Ti_4O/Cu_4Ti_3/Ag-Cu eutectic+rich Ag phase+Ti soild solution for bonding temperature below 1 123 K. For bonding temperature of 1 173 K, the interface structure is Al_2O_3/Cu_3TiO_5+CuAl_2O_4/Cu_4Ti_3/rich Ag phase. Strength of the Al_2O_3/(Ag_ 72Cu_ 28)_ 97Ti_3/Nb joint reaches 189 MPa for bonding temperature of 1 123 K and 18 ks. The lower bonding temperature, or the higher bonding temperature, the lower strength of joints.