The relationships between the sulphide capacity index and the optical basicity,the mole fraction of oxygen ion and the Bell’s ratio were investigated based on extensive lab scale equilibrium and industry scale quasi-equilibrium experimental data in the temperature range of 1300 —1600 C- Although the sulphide capacity index has good relations with different representations of slag basicity,according to the data obtained under the lab scale equilibrium experimental conditions,the similar relations do not exist according to the data obtained under the industry scale quasi-equilibrium experimental conditions.So it is concluded that the sulphide capacity index,which has been considered as a measure of the slag basicity,can not be used for virtually all oxide slags of interest in the field of ironmaking and steelrnaking. The relationships between the sulphide capacity index and the optical basicity, the mole fraction of oxygen ion and the Bell’s ratio were investigated based on extensive lab scale equilibrium and industry scale quasi-equilibrium experimental data in the temperature range of 1300 -1600 C Although the sulphide capacity index has good relations with different representations of slag basicity, according to the data obtained under the lab scale equilibrium experimental conditions, the similar relations do not exist according to the data obtained under the industry scale quasi-equilibrium experimental conditions. so it is that that the sulphide capacity index, which has been considered as a measure of the slag basicity, can not be used for virtually all oxide slags of interest in the field of ironmaking and steelrnaking.