One approach to improving the manufacturing technology of turbomachinery is the application of metal additive manufacturing. Several studies have shown that wire arc additive manufacturing (WAAM) can be used to improve fabrication and reduce the environmental impact of impellers and other components with blades. To further advance manufacturing technology using WAAM, it is necessary to evaluate not only additive manufacturing using a single material, but also additive manufacturing combining multiple materials. However, there are only a limited number of examples of such studies. Therefore, there is a problem in that sufficient knowledge for industrial applications has not yet been obtained. The objective of this study is to evaluate the mechanical properties of a multi-material, stainless steel SST316L and nickel-based alloy, Inconel 718, fabricated by WAAM, when applied with heat treatment. To fabricate the test piece, a wall combining the two materials was fabricated by additively manufacturing an Inconel 718 wall made via WAAM and then additively manufacturing a SST316L wall on top of the Inconel 718 wall made via WAAM. A test piece was obtained by cutting out tensile test specimens from the wall. The specimens were subjected to several types of heat treatments and tensile tests were performed to analyze differences in their mechanical properties. The heat treatments were solution heat treatment, which is generally used for austenitic stainless steels, and aging treatment, which is generally used for Inconel 718. As a result, it was found that the multi-material under any of the heat treatments has mechanical properties that can be concluded to be industrially applicable.