Desulfurization and deoxidation with magnesium is an attractive method to obtain ultra low sulfur and oxygen steel. However, conventional desulfurization and deoxidation processes with magnesium shows that the reaction efficiency of magnesium is not so high, and the use of magnesium powders in metallic form is high in price and risky to handle due to its explosive evaporation. Recently, our laboratory has proposed a new method of desulfurization and deoxidation with magnesium vapor in-situ produced by the carbothemic or aluminothemic reduction of magnesium oxide. This process can decrease the sulfur and oxygen concentration in molten iron rapidly to an ultra-low level with low cost as well as easy and safe operation.