Taylor dispersion is used to measure mutual diffusion coefficients for aqueous Li2SO4 solutions at concentrations from 0.09 to 2.62 mol-dm-3 at 25°C. The Li2SO4 results and previously reported diffusion coefficients for aqueous Na2SO4 and K2SO4 are compared with predictions made by treating the limiting electrolyte diffusion coefficients as reference values and applying corrections for nonideal solution behavior, ionic hydration, and viscosity changes as the concentration is raised. Good agreement is obtained if the M+ + SO 4 2- ⇋ MSO 4 - (M = Li, Na, K) association equilibria are included in the analysis. Extents of formation of the MSO 4 - ion pairs are evaluated by fitting Pitzer's mixed electrolyte equations for aqueous M+–MSO 4 - –SO 4 2- ions to osmotic coefficient data. Diffusion coefficients for hypothetical solutions of the completely dissociated M2SO4 electrolytes are calculated to illustrate the effects of ion association on diffusion. Association of the M+ and SO 4 2- ions increases the overall mobility and thermodynamic driving forces for their diffusion.