In order to promote recycling of ferrous scrap which contains Sn as one of tramp element impurities, removal of Sn from molten steel has been investigated in the present study. Although it has been known that Sn is not easily removed by oxidation refining, Sn can be evaporated as Sn(g) and SnS(g), respectively. Increasing [%S] thus accelerates the de-tinning rate. In the present study, it was elucidated that, under the chemical reaction rate controlling regime, the reaction rate is 1st-order with respect to [%Sn] or 2nd-order with respect to [%Sn]×[%S], depending on [%S] in steel. It was found that surface segregation of S should be considered in the development of the rate equation, and there is also a residual de-tinning reaction rate at high [%S] in molten steel. A unified de-tinning rate model has been developed which is able to calculate the total de-tinning rate, as well as individual rates in the form of Sn(g) and SnS(g) removal, respectively. The relation between the individual de-tinning rate and partial pressure of each gas component is also discussed.