The electrostrictive effect was investigated in Pb(Mg1/3Nb 2/3)O3-xPbTiO3 (PMN-xPT) relaxor ferroelectric crystal, a representative high performance piezoelectric material, with respect to orientation, temperature, and composition. The electrostrictive coefficients Q 11 C, Q 12 C, and Q 44 C of PMN-xPT (x 0.25-0.37) crystals were found to be on the order of 0.055, - 0.024, and 0.020 m4/C2, respectively. The maximum and minimum Q 33 were found to be along 100 and 111 directions, being about 0.055 and 0.014 m4/C2, respectively, showing a strong anisotropic behavior, which is inherently associated with the oxygen-octahedra structure. In contrast to piezoelectric and dielectric responses, the electrostrictive coefficients Q are found to be insensitive to the ferroelectric phase transition, no matter it is induced by the temperature or composition. © 2013 AIP Publishing LLC.