The interaction between γ-aminopropyltriethoxysilane and montmorillonites with different heat-treated temperatures in ethanol-water system was investigated. Samples were characterized by using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis and nitrogen adsorption-desorption i- sotherms. Result suggested that most of the silane molecules existed in the interlayer of montmorillonite and a few of them were grafted on the edge of the layers. The loading amount of silane was respected with the water contents in the interlayer spaces of montmorillonite. Heat treatment reduced the interlayer water contents and consequently affected the grafting reaction. The process of grafting started with the ion exchange of silane molecules With the cation in the interlayer spaces of montmorillonite, and these molecules were adopted bilayer arrangements. Then the hydrolyzed silane molecules were condensated with each other. Owing to the inhibition of ethanol to the hydrolysis of silane and the distance between the adjacent charge sites of the layers, the residual Si-O-Si cross-linked network constituted a ＂pillar＂ structure. These modified products were hydrophobic and had the similar specific surface areas of montmorillonites.