Abstract. In this study, effect of zinc-coated layer on steel sheet of dissimilar metals welding between SCGA270C steel and A5052 aluminum alloy by GTAW was investigated. In the experiments, two types of self-brazing welding; 1) welding between non-zinc-coated steel/aluminum alloy, and 2) welding between zinc-coated steel/aluminum alloy, were carried out. The lap joint configuration in which steel was lying on top of aluminum alloy was applied. From the results of zinc-coated steel case, the reaction between the lowmelting-point zinc with both molten and solid aluminum alloy provided larger welding width between two metal sheets. Moreover, zinc, which is heavier than aluminum alloy, was fallen down but not well mixed into molten aluminum alloy. Consequently, thick intermetallic compound layer near welding interface between steel/aluminum alloy was formed. Comparison of load resistance between non zinc-coated case and zinc-coated steel case, the wider welding width which consequently improvement the load resistance of the welds was obtained, when using low heat input. However, when applying higher, significant contraction of aluminum welding pool promoted crack along the non-uniform chemical composition zone in case of zinc-coated steel. These cracks were the cause of reduction of load resistance of the welds between zinc-coated steel/aluminum alloy.