A Mn-containing galvannealed steel sheet, comprising a steel sheet containing, on a mass% basis: C: 0.03% to 0.35%; Si: 0.01% to 2.00%; Mn: 3.0% to 8.0%; Al: 0.001% to 1.000%; P: 0.10% or less; S: 0.01% or less, and optionally one or more elements selected from: B: 0.001% to 0.005%; Nb: 0.005% to 0.050%; Ti: 0.005% to 0.080%; Cr: 0.001% to 1.000%; Mo: 0.05% to 1.00%; Cu: 0.05% to 1.00%; Ni: 0.05% to 1.00%; and Sb: 0.001% to 0.200%, the balance being Fe and incidental impurities, the steel sheet having a zinc coated layer on one or both surfaces thereof with a coating weight of 20 to 120 g/m 2, wherein the zinc coated layer contains any one of a) to e) described below, a) an oxide containing Fe and Mn, b) an oxide containing Fe and Mn and an Fe oxide, c) an oxide containing Fe and Mn and a Mn oxide, d) an oxide containing Fe and Mn, an Fe oxide, and a Mn oxide, and e) an Fe oxide and a Mn oxide, a total amount of the oxide is 0.01 to 0.100 g/m 2 in terms of an amount of O, a ratio by mass% of Mn to Fe, i.e., Mn/Fe, contained in the oxide is 0.10 to 10.00, the oxide of at least one selected from Fe and Mn is present in an amount of 60% or more in terms of a cross-sectional area fraction in a range from a surface of the zinc coated layer to a position 50% or less of a total thickness of the zinc coated layer, and an oxide of at least one selected from Fe and Mn is present in a surface layer portion of the steel sheet in an amount of 0.040 g/m 2 or less, not including zero, in terms of an amount of O, the surface layer portion of the steel sheet extending from a surface of the steel sheet underlying directly below the zinc coated layer to a position 5 μm or less from the surface thereof. C: 0.03% to 0.35%; Si: 0.01% to 2.00%; Mn: 3.0% to 8.0%; Al: 0.001% to 1.000%; P: 0.10% or less; S: 0.01% or less, and B: 0.001% to 0.005%; Nb: 0.005% to 0.050%; Ti: 0.005% to 0.080%; Cr: 0.001% to 1.000%; Mo: 0.05% to 1.00%; Cu: 0.05% to 1.00%; Ni: 0.05% to 1.00%; and Sb: 0.001% to 0.200%, the steel sheet having a zinc coated layer on one or both surfaces thereof with a coating weight of 20 to 120 g/m 2, wherein the zinc coated layer contains any one of a) to e) described below, a) an oxide containing Fe and Mn, b) an oxide containing Fe and Mn and an Fe oxide, c) an oxide containing Fe and Mn and a Mn oxide, d) an oxide containing Fe and Mn, an Fe oxide, and a Mn oxide, and e) an Fe oxide and a Mn oxide, a) an oxide containing Fe and Mn, b) an oxide containing Fe and Mn and an Fe oxide, c) an oxide containing Fe and Mn and a Mn oxide, d) an oxide containing Fe and Mn, an Fe oxide, and a Mn oxide, and e) an Fe oxide and a Mn oxide, a total amount of the oxide is 0.01 to 0.100 g/m 2 in terms of an amount of O, a ratio by mass% of Mn to Fe, i.e., Mn/Fe, contained in the oxide is 0.10 to 10.00, the oxide of at least one selected from Fe and Mn is present in an amount of 60% or more in terms of a cross-sectional area fraction in a range from a surface of the zinc coated layer to a position 50% or less of a total thickness of the zinc coated layer, and an oxide of at least one selected from Fe and Mn is present in a surface layer portion of the steel sheet in an amount of 0.040 g/m 2 or less, not including zero, in terms of an amount of O, the surface layer portion of the steel sheet extending from a surface of the steel sheet underlying directly below the zinc coated layer to a position 5 μm or less from the surface thereof.