In order to understand the protective properties of the sandstone surface after being treated with methyl-trimethoxysilicane, some badly wind-decayed sandstone samples from grotto in Sichuang Province were selected for experiments. A series of experiments was conducted to test the water - resistance, ventilation and anti- aging properties. Experiments included water – soaking, exposure to acid fog and ultraviolet ray and decaying cycles damage texts. The research showed that the sandstones treated with methyl- trimethoxysilicane have much better water – resistance and anti - aging properties but no obvious changes on ventilation. Cracks were observed on the surface of one stone treated with methyltrimethoxysilicane. Our experiments suggested that the water - resistance and anti – aging properties of stones treated with methyltrimethoxysilicane have been improved, but the decaying cycle damage test showed the treatment might bring negative effect to the treated stone. We concluded that methyltrimethoxysilicane should be used with care.