Intermolecular forces between 18-crown-6 and guest ions have been measured by atomic force microscopy using AFM tips modified chemically with an alkylsilane derivative having 18-crown-6 moiety. The greater adhesion forces were observed with the crown-ether modified tip than with bare tips on mica substrate in aqueous solutions containing K+, probably due to the complexation between 18-crown-6 moiety on tip and K+ in solution. Specific interactions based on cation complexation of 18-crown-6 have been observed in ethanol on mica substrate treated with (3-aminopropyl)triethoxysilane (-NH3+).