The compatibility behaviour of melt-mixed blends of poly(ethylene-co-vinyl alcohol) (EVOH)/ionomer was studied in the complete composition range using tensile, dynamic mechanical, thermal, spectroscopic and morphology characterization techniques. The binary blends were mechanically compatible especially when equilibrated to ambient humidity levels. The above techniques were also applied to characterize the ternary HDPE/ionomer/EVOH where the ionomer plays the role of the compatibilizer due to specific interactions (to the EVOH) and athermal mixing with the polyolefin. Morphology examination showed that EVOH is distributed within the PO matrix in laminar form making the polymeric alloy suitable for gas barrier applications.