Solid-liquid equilibrium (SLE) values were experimentally determined for the NaCl-NH4Cl-H2O system in the temperature range from 293.15 to 333.15 It, using the now-cloud-point method (Zhang et al., 1998, Journal of Chemical and Engineering Darn, 43, 32-37). A judicially selected equilibrium constant of NH4Cl which is consistent with the available literature values, was used to determine a new Pitzer interaction parameter for pure NH4Cl. This new parameter, together with the Pitzer mixing parameters determined from correlating the experimental values obtained in this work and some of the literature values, could be used to extend SLE For this system from 273.15 to 373.15 K, satisfying the process simulation requirement involved in the production of soda.