Abstract: Objective The aim is to investigate on microstructure characteristics and mechanical properties of electron beam welded joints of FGH99 and GH4169 superalloys before and after heat treatment. Methods Microstructure characteristics of welded joints were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and mechanical properties of welded joints at room temperature and high temperature of 650 ℃ were tested as well. Results The results show that welded joints have no obvious defects. Weld zone is composed of coarse dendritic grains, and heat affected zones on both sides are composed of equiaxed grains. After heat treatment, a large number of carbides are precipitated from weld zone and heat affected zones on both sides of welded joints. Among them, γ' phases are precipitated in heat affected zone on the FGH99 side, and δ phases are precipitated in heat affected zone on the GH4169 side. Microhardness of welded joints is lower than that of FGH99 base metal and higher than that of GH4169 base metal. After heat treatment, microhardness is significantly increased, which is mainly attributed to the formation of carbides and precipitated phases. Tensile strength of heat-treated joints at room temperature is approximately 1 403.7 MPa, yield strength is approximately 1 190.3 MPa, and elongation is approximately 21.5%, in which strength and plasticity are comparable to those of GH4169 base metal. Tensile strength of heat-treated joints at 650 ℃ is approximately 1 000.3 MPa, yield strength is approximately 817.3 MPa, and elongation is approximately 15.7%, in which strength and plasticity are significantly lower than those of GH4169 base metal. Conclusion The heat treatment system selected in this study can enable room temperature properties of FGH99/GH4169 dissimilar superalloy electron beam welded joints to reach a level comparable to those of GH4169 base metal, but high temperature mechanical properties are lower than those of GH4169 base metal.