Abstract: Duplex stainless steel (DSS) SAF2205 and micro-alloyed steel X65 were welded by metal inertia gas welding (MIG) with ER2209 welding wires, and the welded joints have good mechanical properties. The type II boundary close to the fusion line at the micro-alloyed steel side was observed by SEM. Obvious concentration gradients of Ni and Cr exist in the region between the two boundaries, where the hardness is much higher. The mechanical properties of the welded joints were investigated by using smooth and notched tensile test and low temperature impact test, and the polarization curves of different weld regions were also tested in 1 mol·L^-1 NaCl solution. The notched tensile strength and impact toughness of the welded metal are lower than those of DSS base metal, but the corrosion potential is higher. The mechanical properties of X65 heat-affected zone (HAZ) is as good as the base metal and the corrosion potential is higher.