The ac field dependence of dielectric and piezoelectric response of sol-gel derived Pb(Zr,Ti)O(3)thin films is presented. The nonlinear response of dielectric polarisation and piezoelectrically induced strain at sub-switching fields was studied in terms of amplitude and phase angle of first and third harmonic. The experimental results have shown that a description by a classical polynomial approach cannot account for many features of observed behavior. However, a model based on the pinning of domain walls on randomly distributed pinning centers seems to describe many features of the experimental data.