An atomic force microscope (AFM) is a very powerful tool to evaluate interaction forces between surfaces in liquids on the molecular scale, but the apparatus was not designed to measure forces in equilibrium. Hence, data obtained by AFM are not in equilibrium in principle. Here we propose a static method to obtain interaction forces between stationary surfaces in aqueous solutions using AFM. The validity of the proposed method was confirmed by comparing interaction forces measured by this method with those by the normal dynamic method for the system of a mica plate and a silica particle in electrolyte solutions where an equilibrium was nearly achieved because water molecules and ions moved much faster than surfaces, The applicability of this method to the measurement of hydrophobic attraction was then examined, and important information on the attraction was obtained. (C) 2001 Academic Press.