The Zn-Mg alloy-plated steel sheet comprises a steel sheet, a Zn-Mg alloy plating layer formed on the surface of the steel sheet and containing 10 to 70 mass% of Mg and the balance of Zn and impurities, A corrosion product layer formed on the surface of the alloy plating layer and containing either a Mg salt of a carboxylic acid having 4 to 20 carbon atoms and an Mg salt of an alkanesulfonic acid having 4 to 20 carbon atoms; Wherein the corrosion product layer contains an alkali metal salt of the carboxylic acid when the corrosion product layer contains the magnesium salt of the carboxylic acid and the corrosion product layer contains the magnesium salt of the alkanesulfonic acid, Wherein the alkali metal salt of the carboxylic acid or the alkali metal salt of the alkali metal salt of the alkanesulfonic acid contained in the chemical conversion treatment layer is at least one selected from the group consisting of Li, Na, K, Rb Is at least one member selected from the group consisting of Cs.
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