The susceptibility profile of thin ferroelectric films was calculated in this paper from Landau phenomenological theory. The dependence of mean susceptibility on the film thicknessLwas discussed. Depending on the parameter δ, the so-called “extrapolation length” which measures the strength of the coupling in the surface layer, two different results are obtained. For δ>0, a size driven phase transition was suggested. Near the critical thicknessLo, the mean dielectric susceptibility can be expressed as Xf' Xb[1 + Co/(L - Lo)]. For δ>0, the mean susceptibility decreases logarithmically with the decrease in film thickness.