The adhesion characteristic of surfaces of SiO2 and the self-assembled film of octadecyltrime-thoxysilane (OTE SAM) on the surface of SiO2 under the relative humidity of 5%—99% were studied using atomic force microscopy/friction force microscopy.Experimental results indicate that the adhesion force of SiO2 increases first with the relative humidity and then decreases sharply.However,the adhesion force of OTE SAM surface hardly changes with the relative humidity due to its strong hydrophobe property.The mechanism of the adhesion force changing with the relative humidity has been analyzed from the viewpoint of surface tension,van der Walls force,and basic bond forces.