A type of magnesium alloy that is capable of producing negative potential, characterized in that it contains 8 wt %.about.9.1 wt % of aluminum (Al), 0.1 wt %.about.1.0 wt % of zinc (Zn), 0.1 wt %.about.1.0 wt % of manganese (Mn), 0.05 wt % or less of silicone (Si), 0.002 or less of iron (Fe), 0.0012 wt % or less of copper (Cu), 0.0009 wt % or less of nickel (Ni) and 0.0008 wt % or less of beryllium (Be), the negative potential magnesium alloy binds with calcium ions and magnesium ions to show a pH value of water quality on the alkaline side.