The mineral dissolution sensor system using GMR-SV and glass/Mg(200 nm) was prepared and characterized. The magnetic field sensitivity of GMR-SV to microscopic magnetic variation was about 0.8%/Oe. The change that occurs when Mg-film dissolves in water, the solubility of water, which is one of the basic properties of mineral water, was sensed by measuring the subtle variation of an electric current. In the case of edible water with Mg mineral added, bubbles were generated on the surface of the Mg film in the first 45 minutes, and the number of drops that were dissolved more rapidly than with the tap and DI waters later reduced to zero. For the edible water samples that each had different mineral Mg concentrations, the Mg solubility speed significantly differed. After injecting Mg film into the edible water, the magnetoresistance of the output GMR-SV signal decreased from a maximum of $45.4;{Omega}$ to a minimum of $43.6;{Omega}$. The measurement time was within 1 min, giving the rate of change ${Delta}R/{Delta}t=0.18;{Omega}/s$. This measurement system can be applied to develop a mineral Mg solubility GMR-SV sensor that can be used to sense the change from edible water to reduced alkali.