The effect of non-stoichiometric ordering on the electrostriction of Pb(Mg-1/3Nb(2)/3)O-3-PbTiO3 (PMN-PT) compositions (65/35) close to morphotropic phase boundary (MPB) has been studied using electrically induced strain and polarization methods. La was substituted (1 to 10 at %) on the A-site to control the degree of B-site cation ordering. The charge imbalance due to La3+ was compensated by two different mechanisms: (1) creation of B-site vacancies, and (2) changing the B-site cation ratio. Electrostriction coefficient measurements revealed dependencies on the degree of non-stoichiometric ordering and the charge compensation mechanism. A high value of the electrostriction coefficient was found to be accompanied by larger electrically-induced strains and smaller polarizations. In addition, the temperature dependence of the electrostriction coefficient was studied.