Relaxor ferroelectrics (0.94 − x)(Bi0.5Na0.5)TiO3–0.06BaTiO3−x(Sr0.7Bi0.2□0.1)TiO3 (BNT–BT–xSBT) (0 ≤ x ≤ 0.5), were prepared by a solid-state reaction process, and their structures were characterized by the transmission electron microscopy and Raman spectroscopy. The BNT–BT–0.3SBT has a very high electrostrictive strain S = 0.152% with hysteresis-free behavior, much more than the reported S in other ferroelectrics. S–P2 profiles perfectly follow the quadratic relation, which indicates a purely electrostrictive effect with a high electrostrictive coefficient (Q11) of 0.0297 m4/C2. Even, its Q11 keeps at a high level in the temperature range from ambient temperature to 180°C. The field-induced large electrostrictive strain of BNT–BT–0.3SBT was attributed to the existence of ferroelectric nanodomains.