The pseudopotential theory in conjunction with the thermodynamic perturbation theory is applied to the calculation of the thermodynamic properties of Na-K, Na-Cs and Na-Rb liquid alloys. Two methods of the thermodynamic perturbation theory are used : variational and Weeks-Chandler-Andersen (WCA). The accuracy of the different pseudopotential models in the framework of the variational method is investigated. The most accurate pseudopotential model is used for calculations by the WCA method. The results obtained by the WCA method are in better agreement with the experimental data as compared with the results of the variational method.