Abstract: Ｒevealing the deterioration law of sandstone strength under dry-wet cycles is highly significant for preventing and controlling unstable rocky slope of road engineering． Taking sandstone of a rocky slope in Lanzhou city as the research object，the effects of dry-wet cycles on the deterioration of sandstone with various initial dry densities were analyzed by uniaxial compressive test，tensile test and SEM observation． The results show that the uniaxial compressive strength，elastic modulus，uniaxial tensile strength and their deterioration rate of sandstone are negatively correlated with cycle number． The uniaxial compressive strength，elastic modulus and uniaxial tensile strength are respectively in good exponential correlation with cycle number． Among the same strength parameters， the difference in strength values of sandstone for various initial dry densities decreases with the increase of cycle number． The uniaxial compressive strength，elastic modulus，uniaxial tensile and their total deterioration degree gradually increase with the increase of initial dry density when cycle number is the same． During the increase of cycle number，the microstructure of sandstone changes significantly，and the microstructure difference between sandstone with various initial dry densities decreases gradually． Hence，the effects of dry-wet cycles on sandstone strength are related to cycle number and initial dry density closely

Key words: road engineering, sandstone, dry-wet cycle, strength deterioration, initial dry density