Microstructure evolution and interface characteristics of dissimilar TC4/TB8 titanium alloys subjected to diffusion bonding and aging treatment are investigated. TC4/TB8 alloys plates can be metallurgically bonded at 830°C for 2h under 18MPa. The microstructure of TC4 alloy is composed of fine intergranular β grains and equiaxed α grains due to recrystallization. The α grains characterized by lath-like, granular, and continuous layer morphology are precipitated from β matrix in the TB8 alloy during furnace cooling and aging treatment. Element distribution mapping and line-profile data indicate that Mo atoms diffuse from the enrichment area (TB8) to the depleted area (TC4), while a small amount of Al and V atoms diffuse along an opposite direction. In addition, the behavior of grain growth across the bonded interface is not obvious under the current parameters.