Keeping indoor humidity environment steady with the correct level is very important for ensuring the sustainable and healthy building. Hygroscopic material, which has ability of adsorbing and desorbing moisture from the adjacent air naturally, can be applied to moderate indoor humidity variations without adding energy cost. So far, there are many kinds of hygroscopic materials with good moisture buffering effect, have been applied to building envelope. However, these methods used only an element sample material in a small climatic oven without ventilation, and the ambience air is assumed well-mixed. These evaluation methods are limited to evaluate material self-properties, and they are inadequate to reveal the material's moisture buffering performance in a real room space. In this research, a series of experiments were carried out in climate controlled test chamber with different loading ratio (loading ratio: the ratio of material's furnishing area to room volume) of hygroscopic material, different air change rate and different moisture production rate. The purpose of this paper is to understand humidity variations by furnishing hygroscopic material, as well as to evaluate the moisture buffering effect of building envelope when hygroscopic material is applied in a room scale. Experimental results indicated that the application of hygroscopic material was an efficient way to reduce the amplitude of daily moisture variation. Furthermore, the moisture adsorption / desorption effects decreased exponentially when the ambient air change rate per unit area of hygroscopic material increased. These experimental and analysis results are very useful for the application of hygroscopic material, as well as for the realization of comfortable and healthy indoor humidity environment from design stage.