The influence of different alloying elements on electrical resistivity of binary magnesium alloys (Mg–Al, Mg–Gd, Mg–Sn, and Mg–Zn) was investigated. The results revealed Gd had the largest influence on resistivity and Zn had the lowest heat treatments which were performed on the as-cast alloys; it was found that T4 treatment increased the resistivity and a linear relationship between the solute content and resistivity which was observed. During isothermal ageing, the resistivity decreases monotonously with ageing proceeding due to the depletion of solute atoms from Mg matrix and the formation of intermetallic phases. A phenomenological formula can be used to describe the relationship between the resistivity and the volume fraction of precipitates. With the help of this formula, resistivity can be used to quantify the precipitation kinetics of binary magnesium alloys.