It has been observed in experiments that charging of nanometer-sized porous material can lead to expansion or contraction of this material. This effect can be explained by a change in surface stress as a function of surface electron charge density. Here, we employ ab initio density functional calculations using a mixed-basis pseudopotential approach to study the change in surface stresses, f, as a function of surface charge density, q for Au thin films with (111) and (100) surfaces. The derivative of the surface stress with respect to the charge, ôf/ôq, at equilibrium is related to and can be evaluated from ôμ/ôe of an uncharged slab, where μ is the chemical potential of the slab and e the tangential strain. The responses of the (111) and (100) surfaces to charging are evaluated in this way as −1.86 V and −0.90 V, respectively. The calculated values compare well to experimental observations (−0.9 V).