Oyaishi samples having efflorescence (<i>Iwashio</i>) were observed under a microscope after being kept for two years at different relative humidities (33, 55, 75 and 92% relative humidity). When a sample under a highly humid condition was transferred to a dry environment and kept there for a fairly long time, effloresced salts which had been melted became dry and flaked off from the surface. In the second experiment the moisture content of the sample changed from 5 to 12% according to relative humidity. This means that wet-dry cycles cause large amount of absorption of vapor in stone even without liquid water. Therefore, it is desirable to keep rock-cliff sculptures under a stable condition with small relative humidity changes to avoid salt crystallization decay. -- AATA