An equation and a set of mixing rules for the prediction of liquid density of pure refrigerants and liquified natural gasLNG.multicomponent systems have been developed. This equation uses the parameters of Mathias and Copeman wP.M. Mathias, T.W. Copeman, Fluid Phase Equilib. 131983.91–108x temperature dependentterm for the Predictive-Soave–Redlich–Kwong wT. Holderbaum, J. Gmehling, Fluid Phase Equilib. 701991. 251–265x equation of state and hence it could be used together with this equation. The equation uses a characteristic parameter for each refrigerant; however, if it is not available, a value of zero is recommended. This model gives an average of absolute errors less than 0.42% for the prediction of liquid density of 28 pure refrigerants consisting of 2489 data points and 0.33% for 18 multicomponent LNG systems involving 132 data points. The model parameters were determined from pure component properties and reported. These parameters were then used without any adjustment to predict liquid density of multicomponent LNG mixtures and excellent results were obtained. The model was also compared with other available methods.