The microstructure, phase composition and texture of iron oxides formed during slab preheating and hot rolling operation may affect the process of descaling. A role these microstructural parameters play is not yet well understood. In this paper structure, texture and phase composition of oxides formed on pure iron, low-carbon steel, and Si-steel are systematically investigated by X-ray diffraction texture measurement and the electron back scattered diffraction (EBSD). The experiments are designed to understand the characteristics of oxide under the continuous heating applied in industrial practice. It is demonstrated that the EBSD technique is an excellent tool to visualize the oxide microstructure and microtexture. Iron oxides developed during high temperature oxidation consist of hematite (Fe2O3), magnetite (F3O4), and wustite (FeO). The columnar structure of magnetite and wustite was observed after high temperature oxidation. Detailed characteristics of oxide structure are presented in this paper.