Both experiment and theory have shown that the stress has a notable impact on the polarization of Nd-doped Bi4Ti3O12 films. In this paper, thermodynamic theory is used to study the effect of stress on the dielectric constants of Bi4Ti3O12 films at room temperature with a two-dimensional model. Results indicate that the change of the dielectric constant for a-phase induced by the lattice distortion is far greater than that for c-phase. Considering the domain reorientation, the external tensile stress may lead to an obvious decrease in the effective dielectric constant of Bi4Ti3O12 films. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.