The effect of ion-ion interactions on the structure and dynamics of the sulfate ion in aqueous MgSO4 solution has been studied by polarization-resolved CARS spectroscopy. Depolarization ratio of the totally symmetric S-O stretch band of the SO42- ion was determined accurately for three different MgSO4 concentrations, 0.8, 1.3, 2.5 mol dm(-3). At 0.8 mol dm-3, the observed depolarization ratio was zero as expected from T-d symmetry. On the other hand, small but meaningful non-zero depolarization ratios were obtained at higher concentrations. These non-zero depolarization ratios are interpreted in terms of symmetry lowering of the sulfate ion, which is due to dynamic ion pair formation between Mg2+ and SO42- ions.