PLZT(7.5/70/30) was initially a cubic phase having diffuse phase transition at high temperatures. Sn-sub-stitution for PLZT(7.5/70/30) underwent an irreversible phase transition from cubic to rhom-bohedral structure. However PLZTS(7.5/70/30/y=5 & 10) could be reversibly switched from paraelectric to ferroelectric phase under electric field without showing a significant change in crystal structure. With in-creasing the amount of Sn-substitution the P-E behaviors of the PLZTS became more antiferroelectric which was similar to the effect of La-substitution of PLZT. Our study may suggest that Sn-substitution ef-fectively weakens a formation of long-range order between polar Ti-or Zr- containing octahedra which greatly affects strain properties.