PURPOSE: To obtain the objective galvannealed steel sheet capable of showing stable corrosion resistance after coating by limiting the ruggedness of a roll and the draft at the time of skinpass rolling and executing treatment by an alkaline soln. with high pH added with Ni and Co.

CONSTITUTION: A galvanized steel sheet is subjected to alloying treatment and is thereafter subjected to skinpass rolling at ≤0.8% elongation percentage by a roll having ≤2.5μ surface roughness Ra. Next, it is treated by a alkaline aq. soln. with pH≥12 contg. 0.01 to 0.5wt.% of one or more kinds of Ni and Co. By this skinpass rolling, the ununiformity on the inside part and surface part of the galvannealed layer can be suppressed, and a part or the whole of an oxide layer formed on the surface part of the galvannealed layer by the treatment with the aq. soln. can be melted. Moreover, Ni and/or Co is substitutionary precipitated to convert the surface potential of the plated layer into a noble one, by which the objective galvannealed steel sheet having extremely excellent corrosion resistance after coating can stably be manufactured.