Utilizing electrical resistivity measurements during heating, precipitation behaviors of high Mg contented Al-Mg alloys, which is currently spotlighted as automotive sheet material, has been analyzed. In the attempt to analyze precipitation behavior in detail, electrical resistivity change ratio was differentiated by temperature and acquired DVRC (Differentiation values of electrical resistivity changes). By measuring DVRC during heating, more precise analysis was possible than conventional electrical resistivity measurement. The transformation process of precursor phase, such as G. P. zone, shown as positive peaks at low temperature region in DVRC, was accelerated by higher solid solution treatment temperature. This reaction was identified as being activated by excessive vacancy concentration. With increased heating rate and Mg addition, splitting of DVRC peaks in low and high temperature was observed. This indicates that in high Mg concentrated Al-Mg alloy various precipitation processes highly depend on heating rate and Mg concentration.