The most serious problem in recycling of steel is surface hot shortness during hot deformation due to Cu mixed into steels from scrap. Tin accelerates this effect of Cu. The amount of Cu in steel scrap increases year by year. Several methods have been examined to suppress this shortness. However, it is not easy to separate Cu and Sn from steel scrap using physical and chemical methods and to remove these elements from steels by the current smelting process. Hence, Cu and Sn accumulate in steels with the repetition of recycling. On the other hand, Cu has a potential to increase some steel properties, for instance, strengths and corrosion resistance. This decreases environmental load during the life cycle of steels. Hence the suppression of surface hot shortness due to Cu is important for a decrease in the environmental load by steel. The surface hot shortness occurs through preferential oxidation of Fe atoms during heating for hot deformation and formation of liquid Cu-enriched phase at the steel/scale interface. This Cu-enriched phase penetrates into the steel grain boundaries and causes surface cracks. Therefore, there exist tolerable contents of Cu and Sn in commercial steels. In the present paper, the details of the mechanism of the surface hot shortness are examined in order to find the ways for the suppression of the shortness by controlling microstructures in the vicinity of the steel/scale interface through physical metallurgy. Controlling of microstructures can be performed by alloy designing of steel and controlling of heating temperature, cooling rate and heating atmosphere.