The effect on the polarization of antiferroelectric (AFE) PNZST ((Pb,Nb)(Zr,Sn,Ti)O3) thin films by ε-E (dc bias field) cycles was studied. It was shown that in these films the AFE ordering is destroyed by the application of a dc electrical field bias along the surface normal direction. After removing the dc bias the film relaxes slowly back to the initial AFE state. This phenomenon is dependent on the film thickness. The relaxation time decreases with increasing film thickness. With increasing storage time of the sample after removing the dc bias at room temperature or heat treatment above the Curie temperature, the AFE ordering can return. From the characteristics of hysteresis loops and ε-E behaviours, we can ascertain that this phenomenon could be attributed to the difference in the poled volume at the interfaces between the electrode and the film.