The microstructure, defect characteristics, and mechanical properties of electron beam welded (EBW) tantalum-to-stainless steel joints were investigated. Joint formation was influenced by the position of the EBW heat source. with a well-formed joint was obtained when the heat source was deviated by 0.2 mm towards the stainless steel. The weld is composed of fine dendrites with high elemental Fe content and homogenously-dispersed ε (Fe2Ta) and μ (FeTa or Fe7Ta6) phases. However, ε and μ phases formed at the tantalum fusion line had lamellar distribution and micro-cracks are easily formed in this region under welding stress. Although the weld zone has high hardness, the poor deformation compatibility of the fusion line at the tantalum side and the existence of crack sources lead to fracturing during the tensile test. The tensile strength of the joints was found to be low, 255 MPa