The extended corresponding states principle has been applied on the prediction of the surface tension of pure molten alkali halides. The model uses liquid density and vapour pressure data of the salts of interest and of the reference salt, chosen to be NaCl, as the input for the calculation of temperature-dependent equivalent substance reducing ratios (ESRR). The model here described was already applied on the prediction of the viscosity and thermal conductivity of pure molten alkali halides [High Temp.-High Pressures, 2000]. Calculations were also made using the simple two-parameter corresponding states principle, with the melting, temperature and corresponding density as scaling factors. Agreement between calculated and experimental data is within 10-15% for most of the salts studied.