Abstract: Slightly weathered sandstone in Chongqing area was studied to investigate and quantify the effects of cyclic wetting and drying to the rock strength.The UCS,tensile strength and Young’s modulus were measured after subjecting the sandstones to 1,3,6,10,15 cycles of wetting and drying.The results indicated that the damage of sandstone caused by cycles of wetting and drying is irreversible.UCS,tensile strength and Young’s modulus decrease by 20.73%,51.96% and 33.79%, respectively,after 15 cycles.There was a marked logarithmic relationship between UCS and cycles,so was tensile strength and Young’s modulus.The erosion of sandstone by water caused an inflexion on damage when sandstone was full saturated.