At moderate and high temperature applications, nickel-based superalloys are widely preferred as suitable candidate materials due to their high mechanical properties and corrosion/oxidation resistance, however, difficulties in mass production of these alloys and their cost cause the use of these alloys as a part of dissimilar weld joints with any structural material. In this study, a dissimilar weld joint between a nickel-based superalloy (UNS 10276) and unalloyed steel (SA 516 GR 70) was successfully performed by gas tungsten arc welding method by using ErNiCrMo-3 filler metal. Initially, the microstructural features of base materials, heat affected zone and weld metal were characterized and cellular, coarser cellular and epitaxial growth dendrites as matrix phases and several Mo-rich and Nb-rich precipitates embedded in the solidified structure were observed in weld metal. In heat affected zones and fusion lines of the dissimilar joints, some metallurgical phenomena like partially melted zone, solidification at grain boundary, migrated grain boundary and decarburization were also examined. All these microstructural features affected the mechanical properties.