Relationship between surface structure of hot rolled steel sheets and their galvannealing behavior has been examined using SEM, EPMA and SIMS. Si and P as oxides are enriched at the interface between oxide layers and steel substrates of the hot rolled steel sheets. Quantity of the enriched elements increases as a function of thickness of the oxide layer, namely oxidation time. Some Si oxides remained on the surface, although most of the oxide layer had been removed by dipping them in HCl with a pickling inhibitor. Surface grains of steels as well as the oxide layers were removed in HCl without the pickling inhibitor, but the surface is covered with phosphide of P segregated to the grain boundaries. The segregated P seems to suppress the successive dissolution of the grains. Thick areas of about 0.5 mm diameter have been formed in the coating of the hot rolled steel pickled in HCl with the inhibitor, although the uniform coatings have been formed in the case of the hot rolled steel pickled in HCl without the inhibitor. The thick areas are caused by the anomalous alloying of Zn and Fe present near the Si oxide left on the steel surface.