Molds for precision casting are made by repeating the process of dipping in slurry which consists of fire refractory materials and stuccoing and drying in several times. As rapid drying may cause the mold to crack and peel, the drying time is determined in consideration of the reduction rate of the evaporation components. Although it is considered that the mechanical and thermal properties of green sand mold depend on its moisture content, their relation has not been c1arified quantitatively. Experiments on mechanical strength and thermogravimetry and thermodilatometry were carried out, under the condition in which evaporation components, such as moisture, were contained in the green sand mold. The bending strength of green sand mold containing moisture increases with the decrease of the moisture content ratio. The bending strength of mold is largely influenced by the crystallization of colloidal silica, and rapidly increases more than the crystal melting temperature of silica. The average thermal expansion coefficient of green sand mold containing moisture is negative from room temperature to about 330K, and decreases with increasing moisture content ratio.