Crude high Cr containing steel such as tool steel, heat-resistant steel or stainless steel is produced by dissolution of high carbon ferro-chromium into molten crude steel. In the refining process, decarburization is performed at the first stage, and deoxidation is followed in the next stage. Therefore, the equilibrium relation between dissolved Cr and O in molten Fe-Cr alloy after decarburization is very important when yield of deoxidizer is considered for the overall control and optimization of the process. It is well known that the yield of deoxidizer does strongly depend on the kinds of refractories of furnace in the secondary refining process. In the present work, the equilibrium relation between dissolved Cr and O in molten Fe-Cr alloy has been measured in a Cr 2O 3, MgO or Al 2O 3 crucible at steelmaking temperature. O contents at given Fe-Cr components have been lower in order of Cr 2O 3, Al 2O 3 and MgO crucible. The present results have been discussed based on the activities of the constituents in pure solid Cr 2O 3, and FeO ̇Cr 2O 3, MgOCr 2O 3 and (Al,Cr) 2O 3 solid solutions.