A magnesium alloy sheet made of a magnesium alloy containing Al, comprising: particles of an intermetallic compound containing at least one of Al and Mg, the particles being present in the sheet in a dispersed state, the average size of the particles of the intermetallic compound being 0.5 μm or less, the percentage of the total area of the particles of the intermetallic compound being more than 0% to 11% in a cross section of the sheet; and an oxide film which extends over at least 90% of the surface of the sheet and which has a uniform thickness, wherein in a cross section of the sheet subjected to saltwater corrosion testing, the uniformity defined as the proportion t max /t min is 1 to 30, where t max is the maximum thickness of the oxide film, which is present on the surface of the sheet, and t min is the minimum thickness thereof, wherein the magnesium alloy contains a content of Al of 4.5% by mass of the alloy or more and 12% by mass or less, one or more additives selected from Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, Zr, Ce and rare-earth elements (excluding Y and Ce), the sum of the contents thereof being 0.01% to 10% by mass of the alloy, and balance magnesium and any unavoidable impurities, and wherein the magnesium alloy sheet is obtainable by a method including: (i) a step of preparing a cast sheet, made of the magnesium alloy, produced by a continuous casting process; (ii) a step of solution-treating the cast sheet at a temperature of 350°C or higher to produce a solid-solution sheet; and (iii) a step of hot-rolling the solid-solution sheet at a heating temperature of 300°C or lower to manufacture a rolled sheet. particles of an intermetallic compound containing at least one of Al and Mg, the particles being present in the sheet in a dispersed state, the average size of the particles of the intermetallic compound being 0.5 μm or less, the percentage of the total area of the particles of the intermetallic compound being more than 0% to 11% in a cross section of the sheet; and an oxide film which extends over at least 90% of the surface of the sheet and which has a uniform thickness, wherein in a cross section of the sheet subjected to saltwater corrosion testing, the uniformity defined as the proportion t max /t min is 1 to 30, where t max is the maximum thickness of the oxide film, which is present on the surface of the sheet, and t min is the minimum thickness thereof, wherein the magnesium alloy contains a content of Al of 4.5% by mass of the alloy or more and 12% by mass or less, one or more additives selected from Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, Zr, Ce and rare-earth elements (excluding Y and Ce), the sum of the contents thereof being 0.01% to 10% by mass of the alloy, and balance magnesium and any unavoidable impurities, and wherein the magnesium alloy sheet is obtainable by a method including: (i) a step of preparing a cast sheet, made of the magnesium alloy, produced by a continuous casting process; (ii) a step of solution-treating the cast sheet at a temperature of 350°C or higher to produce a solid-solution sheet; and (iii) a step of hot-rolling the solid-solution sheet at a heating temperature of 300°C or lower to manufacture a rolled sheet. (i) a step of preparing a cast sheet, made of the magnesium alloy, produced by a continuous casting process; (ii) a step of solution-treating the cast sheet at a temperature of 350°C or higher to produce a solid-solution sheet; and (iii) a step of hot-rolling the solid-solution sheet at a heating temperature of 300°C or lower to manufacture a rolled sheet.