A simple approach has been used to calculate the excess entropy of mixing (ΔSxs) of liquid Na-K and Na-Cs alloys as a function of concentration and temperature. The basic ingredients are the entropy of pure liquid metals and the observed volume of mixing. The temperature dependence ΔSxsfor Na-Cs is strikingly diffierent than Na-K- HΔSxsfor Na-Cs first increases withTand then starts decreasing whereas for Na-K it decreases continuously with increasingTaboveTm.