Treatment of very fragile and porous stone in a highly dry condition with potassium silicate was experimentally studied as to its consolidating effect and durability (stability) for the conservation of cave temples in China. The following results were obtained by the experiment: 1) Impregnation with potassium silicate increased the splitting tensile strength of the treated stone 1.5 to 2 times. This consolidation effect was almost the same as the effect gained with acrylic resin and silane, and its durability was as high as that gained with silane; 2) Potassium silicate whose molar ratio of SiO₂ to K₂O is high (4.0) exhibited quite good water resistance, while one whose molar ratio is low (2.6) showed little resistance; and 3) Efflorescence of potassium silicate was extremely dependent upon its molar ratio of SiO₂ to K₂O. The degree of efflorescence of potassium silicate whose molar ratio is 4.0 was far lower than the one whose molar ratio is 2.6. Considering the above results and the fact that the molar ratio of SiO₂ to K₂O is up to 3.8-3. 9 in order to obtain a low viscous and stable aqueous solution of potassium silicate, it can be said that potassium silicate whose molar ratio is 3.8-3.9 is quite a possible consolidant of very porous and fragile stone for the conservation of cave temples in the northwest region of China which has a very dry climate. -- AATA