Abstract: The laser welding of 3 mm thick TC4 titanium alloy/15-5PH stainless steel was carried out with nickel aluminum bronze (NAB) as the transition layer. Effects of adding NAB transition layer on the joint formation, microstructure and mechanical properties were studied. The results show that the laser welding of TC4 titanium alloy/15-5PH stainless steel with NAB transition layer can obtain a well-formed full penetration joint. The tensile strength of the joint is 290 MPa, and the hardness of the interface layer on the titanium alloy side is 547.8 HV. The interface on the titanium alloy side of the joint is composed of three IMCs layers with different morphologies. The number of less brittle Cu-Ti and Ni-Ti phases increases significantly, while the number of highly brittle Ti-Fe phases decreases significantly, indicating that the addition of NAB transition layer inhibits the formation of highly brittle Ti-Fe phases at the interface of titanium alloy side.