A galvannealed steel sheet comprising: a steel sheet; a coating layer on a surface of the steel sheet; and a mixed layer formed between the steel sheet and the coating layer, wherein the steel sheet contains, in terms of mass%, C: 0.050% or more and 0.50% or less, and Mn: 0.01% or more and 3.00% or less, further contains one or more of Si: 0.01% or more and 3.00% or less, Al: 0.010% or more and 2.00% or less, and Cr: 0.01% or more and 2.00% or less, limits amounts of P, S, O, N, Ti, Nb, Mo, Cu, Ni, and B to P: 0.100% or less, S: 0.0200% or less, O: 0.0100% or less, N: 0.0100% or less, Ti: 0.150% or less, Nb: 0.150% or less, Mo: 1.00% or less, Cu: 2.00% or less, Ni: 2.00% or less, and B: 0.0100% or less, satisfies the following Expression 1 when the Mn content, the Si content, the Al content, and the Cr content are respectively expressed by [Mn], [Si], [Al], and [Cr], in terms of mass%, Mn + Si + Al + Cr ≥ 0.4 and contains a remainder including Fe and unavoidable impurities; the coating layer is a galvannealed layer containing, in terms of mass%, Fe: 7.0% or more and 15.0% or less, Al: 0.01% or more and 1.00% or less, and a remainder including Zn and unavoidable impurities; the mixed layer includes a base iron portion having fine grains having a size of greater than 0 μm and equal to or smaller than 2 μm, a Zn-Fe alloy phase, and oxides containing one or more types of Mn, Si, Al, and Cr, and wherein in the mixed layer, the oxides and the Zn-Fe alloy phase are present in grain boundaries that form the fine grains, and the Zn-Fe alloy phase is tangled with the base iron portion. a steel sheet; a coating layer on a surface of the steel sheet; and a mixed layer formed between the steel sheet and the coating layer, wherein the steel sheet contains, in terms of mass%, C: 0.050% or more and 0.50% or less, and Mn: 0.01% or more and 3.00% or less, further contains one or more of Si: 0.01% or more and 3.00% or less, Al: 0.010% or more and 2.00% or less, and Cr: 0.01% or more and 2.00% or less, limits amounts of P, S, O, N, Ti, Nb, Mo, Cu, Ni, and B to P: 0.100% or less, S: 0.0200% or less, O: 0.0100% or less, N: 0.0100% or less, Ti: 0.150% or less, Nb: 0.150% or less, Mo: 1.00% or less, Cu: 2.00% or less, Ni: 2.00% or less, and B: 0.0100% or less, satisfies the following Expression 1 when the Mn content, the Si content, the Al content, and the Cr content are respectively expressed by [Mn], [Si], [Al], and [Cr], in terms of mass%, Mn + Si + Al + Cr ≥ 0.4 and contains a remainder including Fe and unavoidable impurities; C: 0.050% or more and 0.50% or less, and Mn: 0.01% or more and 3.00% or less, further contains one or more of Si: 0.01% or more and 3.00% or less, Al: 0.010% or more and 2.00% or less, and Cr: 0.01% or more and 2.00% or less, limits amounts of P, S, O, N, Ti, Nb, Mo, Cu, Ni, and B to P: 0.100% or less, S: 0.0200% or less, O: 0.0100% or less, N: 0.0100% or less, Ti: 0.150% or less, Nb: 0.150% or less, Mo: 1.00% or less, Cu: 2.00% or less, Ni: 2.00% or less, and B: 0.0100% or less, satisfies the following Expression 1 when the Mn content, the Si content, the Al content, and the Cr content are respectively expressed by [Mn], [Si], [Al], and [Cr], in terms of mass%, Mn + Si + Al + Cr ≥ 0.4 and contains a remainder including Fe and unavoidable impurities; the coating layer is a galvannealed layer containing, in terms of mass%, Fe: 7.0% or more and 15.0% or less, Al: 0.01% or more and 1.00% or less, and a remainder including Zn and unavoidable impurities; Fe: 7.0% or more and 15.0% or less, Al: 0.01% or more and 1.00% or less, and a remainder including Zn and unavoidable impurities; the mixed layer includes a base iron portion having fine grains having a size of greater than 0 μm and equal to or smaller than 2 μm, a Zn-Fe alloy phase, and oxides containing one or more types of Mn, Si, Al, and Cr, and wherein in the mixed layer, the oxides and the Zn-Fe alloy phase are present in grain boundaries that form the fine grains, and the Zn-Fe alloy phase is tangled with the base iron portion. a base iron portion having fine grains having a size of greater than 0 μm and equal to or smaller than 2 μm, a Zn-Fe alloy phase, and oxides containing one or more types of Mn, Si, Al, and Cr, and wherein in the mixed layer, the oxides and the Zn-Fe alloy phase are present in grain boundaries that form the fine grains, and the Zn-Fe alloy phase is tangled with the base iron portion.