In the present work, the densities of a mould flux slag were measured as a function of temperature by electrostatic levitation (ESL) method. The density of a mould flux, as measured by ESL method decreased linearly with increasing temperature. The results obtained are compared with the value measured by the sessile drop method just above the melting point of the slag. The discrepancies are explained on the basis of the inherent merits and demerits of the two types of measurements. The experimental values of present work were also compared with the density data for other mould flux slags from Swedish plant practice, obtained by the sessile drop method as part of the present work as well as literature data. A thermodynamic model of molar volume, developed in the present group was used to predict the density of slags. The molar volume was described as a function of integral molar enthalpies of mixing. In the case of ternary systems corresponding to the mould flux slag, the calculated values are in reasonable agreement with the experimental values.