Melt flow properties, solution behavior, and mechanical properties of the sulfonated EPDM ionomers obtained by sulfonation of high molecular weight EPDM in the presence of a phase transfer catalyst were studied. The results showed that these ionomers can be processed more easily than those obtained by sulfonation without a phase transfer catalyst. Addition of zinc stearate lowered the melt viscosity, represented by the torque value of a Brabender torque rheometer, and increased both the flow activation energy and the tensile strength. Both melt viscosity and tensile strength increased with sulfonate content of the ionomer up to 30 meq/100 g. An increase of neutralization degree barely affected the melt viscosity and flow activation energy, but enhanced the tensile strength up to an equivalent ratio of 2 and also lowered the solution viscosity. Cations used in neutralization exerted significant influence on the properties of the ionomers. For monovalent cations, melt viscosity and tensile strength decreased with decreasing ionic potentials, while for divalent cations, with increasing ionic potentials and with decreasing covalent character, tensile strength decreased but melt viscosity increased. The order of decreasing solution viscosity was almost the same as that of melt viscosity, except for the reversal of Ca and Mg. Addition of ethyl alcohol decreased the solution viscosity of the ionomer, while addition of ethylene glycol increased the solution viscosity.