Ammonia is widely used as a refrigerant in absorption systems. Water is used as a solvent. For an adequate and accurate analysis of an absorption system’s performance, it is important to be able to determine the thermodynamic properties of such a refrigerant-absorbent solution. This paper presents a set of seven polynomial forms of property correlations developed based on experimental data. The developed correlations are simple, easy to use, and explicitly defined, and they best describe the thermodynamic properties of an ammoniawater mixture. Also, this paper presents the results of the developed correlations compared with the results of other correlations reported in the literature.