Phase change materials (PCMs) are promising alternative materials for a variety of thermal energy storage and related applications. In this work the effect of environmental humidity on properties of molten salt phase change materials was studied by putting different PCMs in different humidity. The results of differential scanning calorimeter (DSC) analysis showed that humidity environment has little effect on the latent heat and onset melting point of these PCMs. SEM micrographs illustrated the effects of water vapor on surface morphology of different phase change materials. The results of thermal constant analysis suggested that humidity affects the thermal conductivity of some salts. But this effect is basically invariable, and will not change with the increase of humidity.