The purpose of this study is to put the 37Ni-6Mn-10Cr type weld metal to practical application for the gas metal arc (MIG) welding of 9Ni steel. The effect of molybdenum, tungsten, and nitrogen on the strength and notch toughness of weld metal and the effect of silicon and sulfur on the hot crack sensitivity were examined. Then the joint efficiencies of MIG weldments made with an optimum level of filler wire chemical composition were examined varying heat input of welding and plate thickness. The center-notched wide plate tension test was conducted in order to assertain the satisfactory performance of this filler wire in comparison with the conventional 70Ni type filler wire. This filler wire is applicable for Ar-Co2 gas shielded arc welding, which produces stable arc and good penetration, thus preventing from occurrence of lack of fusion.