The law of corresponding states of molten salt mixtures that include unsymmetrical salts was developed. The corresponding states equations for the thermodynamic and transport properties were obtained by expanding the Helmholtz free energy and the transport properties in terms of differences of the pair potential parameters, difference of the ionic size, and difference of the ionic mass. The effect of valences on the properties was accounted for by the products of cation and anion valences in the corresponding states equations. Equations for the mixing molar volume, surface tension, electrical conductivity, and viscosity were derived from the corresponding states equations. The estimated mixing properties satisfactorily agreed with the observed ones.