During the treatment in the steel ladle the intended mass transfer between the steel and the slag occurs, but the unintended mass transfer between the refractory and the slag takes place too. The aim of this work is to determine the mass transfer coefficient between steel and slag as well as for refractory and slag. A model for the mass transfer between liquid phases is developed; it is based on the wall treatment for species transport and Fick’s second law. For the mass transfer steel-slag and refractory-slag dimensionless power laws are deduced. It could be shown that the mass transfers steel-slag as well as refractory-slag increase with increasing purging gas flow rates and slag bath height as well as with decreasing viscosity. For the evaluated steel ladle purging gas flow rates of 260 and 300 Nl/min were identified as optimal process conditions.