There are provided a magnesium alloy coil stock having good flatness and a method for producing the magnesium alloy coil stock, and a magnesium alloy structural member that uses the coil stock and a method for producing the magnesium alloy structural member. The coil stock is obtained by coiling a sheet composed of a magnesium alloy in a cylindrical shape, and the internal diameter of the coil stock is 1000 mm or less. The coil stock can be produced by rolling a cast material obtained by subjecting a magnesium alloy to continuous casting, subjecting the rolled sheet to warm leveling, and coiling the worked sheet in a cylindrical shape while the temperature just before coiling is decreased to 100° C. or less.