For industrial purposes, the adhesion control of secondary scale on hot rolled steel sheet is important. A basic study was carried out to clarify the effect of scale microstructure on the scale adhesion of low carbon steel (0.03%C-0.2%Mn). When scale of FeO (about 8 mu m thickness) was generated at 800 degrees C and transformed by continuous cooling from 250 similar to 600 degrees C to 200 degrees C, the scale transformed from 400 degrees C showed good adhesion. The scale consisted of magnetite seam from the steel substrate, lamellar structure of magnetite and alpha-Fe, and magnetite layer from the scale surface. The orientation analysis by TEM showed the relationship {110}Fe//{100}Fe(3)O(4), < 110 > Fe//< 100 > Fe(3)O(4), and the lattice strain was calculated as 4%. On the other hand, FeO/Fe substrate showed the relationship {100}Fe//{110}FeO, < 110 > Fe//< 110 > FeO, and 25% lattice strain was calculated. It is considered that the adhesion of scale should be affected by the lattice strain, thus Fe(3)O(4)/Fe substrate showed better adhesion than FeO/Fe substrate. The temperature of FeO formation also affects the scale adhesion through the extent of Fe super saturation in FeO.