Molecular adsorption on a microcantilever surface causes the cantilever to bend as a result of adsorption-induced stresses. A model for adsorption-induced surface stress based on atomic or molecular interaction is proposed. The model was tested with mercury adsorption on gold-coated cantilevers. Calculated deflections based on the proposed simulation model agree well with measured deflection data. This model gives insight into the interatomic forces that play a significant role in creating adsorption-induced surface stresses and resultant mechanical bending of microcantilevers.