Die soldering is one of common defect generating during the die casting process of aluminum alloys. Until now, the various researchers have been usually studied about die soldering phenomenon in relation to the aluminum components. However, the influence of the mold materials was rarely studied. So, in this study, we have carried out the die-soldering tests using both STD61 and S45C steel to confirm the effect of die materials on die-soldering. Each Aluminum alloys were melted and held at 680 °C and then STD61 and S45C steel were dipped for 2 hr in the aluminum melt. After dipping , the substrate was cooled in the air and analyzed using a SEM and EPMA. The result of soldering test, reaction layer of STD61 substrate has increased according to Si contents of aluminum, however, reaction layer thickness was deceased in the S45C substrate. †(Received June 25, 2013)