Interaction forces between a cleaved mica and the SiO2 surface of an apes of an AFM probe in electrolyte solutions mere measured using an Atomic Force Microscope (AFM). It is found that (1) the AFM is a powerful apparatus to measure in-situ the interaction forces between surfaces in solutions on the molecular Level, (2) the long-range interaction force between surfaces is estimated well by the classical DLVO theory, (3) the magnitude of the short-range interaction force corresponds to the order of the hydration enthalpy of the ions in the solution. A possible model for the structure of water molecules and ions adsorbed on the surface was discussed.