Abstract: Hot isostatic pressing (HIP) was used to join two dissimilar aerospace alloys, namely Al12A12 and Ti6Al4V, for the first time. The microstructure and compositional evolutions were evaluated in the joint interface by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The microhardness and shear strength tests were applied to study the mechanical properties of the joints. As a result, different intermetallic compounds (e. g., Al₃ Ti, TiAl₂, and TiAl) form in the reaction layer of Ti/Al. The findings show that the microhardness value of the joint region is 163 HV. The highest strength in the bonding zone is 23 MPa, which exhibites a 17.9% improvement compared to that only with Cu coating, but is lower than the bonding strength with the interlayer. The fracture mode is brittle fracture due to overburden and void formation. The elements of dissimilar materials diffuse into each other during the HIP. Furthermore, various intermetallic compounds form at the interface, which affects the mechanical properties of the joints.