Daily average analysis of slag and the corresponding hot metal samples were collected on a 1033 m3 blast furnace of the Egyptian Iron and Steel Company (EISCO) over a period of 50 days during May to June 2019. The measured temperature is that of liquid hot metal. The data obtained are used to study sulphur distribution between slag and metal using the concept of slag capacity. The partial pressure of oxygen is indirectly estimated by applying the thermodynamics of manganese oxidation reaction. The results show that the activity coefficients of Sulphur and manganese in the metal are 3.575 and 0.5193 respectively. There is a linear relationship between activity and concentration of MnO in the slag. Calculated and measured sulphur distribution coefficients are in satisfactory agreement.