Spheroidal graphite cast iron welded joints were made by TIG using 5 Fe-Ni welding rods ; 83 Fe-10 Ni, 73 Fe-20 Ni, 63 Fe-30 Ni, 53 Fe-40 Ni and 43 Fe-50 Ni. By investigating the Vickers hardness and microstructure of the welded joints in the welded boundary layer, weldability is estimated. Then, to clarify the reliability of the welded joints, tensile and fatigue tests using the welded joints and base metal were also carried out, and the tensile strength and S-N curve obtained from these tests were compared. The results showed that the 5 Fe-Ni welding rods used are effective in preventing the formation of white cast iron during welding, and that the fatigue limit of the welded joint using the 73 Fe-20 Ni welding rod is equal to that of the base metal.