Abstract: A sample is taken out of a molten magnesium alloy, the cooling curve of the sample during solidification is measured, the content of the aluminum component in the sample is determined by the use of the crystallization temperature of a phase appearing in the cooling curve, together with cooling curves, and if the results of bath analysis show the components to deviate from the standard values and target values, an aluminum-manganese master alloy, aluminum or magnesium is added to the molten magnesium alloy to adjust the components to an appropriate amount of aluminum or an appropriate iron/manganese ratio, whereby a magnesium alloy is produced.