Recently the soldering iron tip has been severely damaged by molten Pb-free solders during operation due to the high reaction rate of metals in molten lead-free solder. The tip is usually protected by plated iron to prevent the direct contact of copper with molten solders. However, the plated iron tip is heavily dissolved into molten Pb-free solders and the life time of the iron tip is reduced. In this study the simple reaction test between Sn-3.0Ag-0.5Cu (mass%) solder and plated iron was carried out to estimate the dissolution of plated iron in molten Pb-firee solder and the effect of the grain size of plated surface on the reaction between Pb-free solder and plated iron. An iron-plated copper was used as the test piece. The Pb-free solder was placed on the test piece and it was put into an oven held at 673, 703 and 733K for 3.6, 10.8 and 32.4ks. After heating, the dissolution thickness of plated iron was measured and the intermetallic compound between Pb-free solder and plated iron was analyzed by XRD. As a result, it has been made clear that the dissolution thickness of plated iron decreases with the decrease of the gain size and then the dissolution of plated iron in molten Pb-free solder is attributable to the grain size of plated iron.