The present study was carried out to evaluate the microstructural and mechanical properties on friction stir welded Inconel 625 alloy. For this work, friction stir welding was performed at a tool rotation speed of 200 rpm and a traveling speed of 100 mm/min. As a result, the grain refinement was achieved from 10.3 μm in the base material to 2.1 μm in the stir zone at an average grain size, accompanied by the dynamic recrystallization. This grain refinement has an effect on the increase of mechanical properties so that microhardness and tensile strength were significantly increased than that of the base material, more than 40% and 15% in fraction, respectively.