In the present research, welding of Inconel 713 superalloy and high strength AISI 4140 steel was successfully implemented by using pulsed Nd:YAG laser. The effect of heat input on the microstructural and mechanical properties of the weld was studied to find the best conditions for achieving a high quality weld. The microstructure characteristics of different weld regions including weld metal and heat affected zone were examined using the optical and scanning electron microscopies. It was observed that a columnar dendritic structure was formed at the edge of weld metal due to higher gradient temperature, while the reduction of gradient at the center of weld metal produced a cellular dendritic structure. The increase of heat input encouraged the formation of coarse dendritic structure which resulted in a reduction in the hardness of weld metal. The HAZ of 4140 steel side showed the maximum hardness for different values of heat inputs due to formation of martensitic microstructure, while the hardness in HAZ of Inconel 713 side was not showed a significant change. The higher value of heat input led to the segregation of Nb, Mo and Ti elements in the inter-dendritic regions and formation of brittle laves phase which resulted in a reduction in the tensile strength. However, the weld joint indicated a maximum tensile strength of 1068 MPa at lower heat input (1875 J/mm). The fracture surface of the tensile specimens showed a brittle fracture in the weld metal at different heat inputs.