As for impregnation treatment of stone with resin, a better effect can be got by a deeper penetration of the resin. The drier the stone, the deeper the penetration of the resin. The author carried out an experimental study on the relationship between the hydrophobic effect of impregnation treatment of stone with silane and its moisture content before treatment. Stone samples were divided into four groups and conditioned so that they have four grades of moisture content. Then, they were impregnated with a solution of an oligomer of methyl tri-ethoxy silane by brushing. The resin contents of the treated stones did not show clear relationship to their moisture contents before treatment. However, their hydrophobicity showed quite clearly a relationship to their moisture content before treatment.