The properties of poly(styrene-co-styrenesulfonic acid) (PSSA) ionomers mixed with NaOH and p-aminobenzoic acid (ABA) were investigated dynamic mechanically. It was found that when NaOH was added to the PSSA+ABA solution to neutralize two acid groups, the properties of the blends were similar to those of Na-sulfonated polystyrene ionomer. In these blend systems, the Na-aminobenzoate probably acted as filler. In the blend of the PSSA polymer and Na-aminobenzoate, it was suggested that the so-called core-shell type multiplets form. However, when Na-sulfonated polystyrene was mixed with the ABA, the ABA molecules acted as a polar plasticizer. It was also found that in the blend system of PSSA+ABA partly neutralized with NaOH, the property fell somewhere between those of the two latter blend systems.