The effect of a sodium ionomer (ion.Na+) on the compatibility of polypropylene (PP)/high-barrier ethylene-vinyl alcohol copolymer (EVOH) blends was studied in terms of the thermal, mechanical, and optical properties and morphology. The rheological behavior, tensile tests, and morphology of the binary blends showed that the miscibility of EVOH with PP was very poor. The miscibility of the polymers improved with the ionomer addition. In general, the ion.Na+ concentration did not alter the thermal behavior of the blends, but it did improve the ductility of the injection-molded specimens. Scanning electron micrographs displayed better adhesion between the PP and EVOH phases in the samples with the ionomer. The mechanical improvement was better in the film samples than in the injection-molded samples. A 90/10 (w/w) PP/EVOH film with 5% ion.Na+ and an 80/20 (w/w) PP/EVOH film with 10% ion.Na+ presented better global properties than the other blends studied. (C) 2004 Wiley Periodicals, Inc.