Three poly(ethylene-ran-acrylic acid)s (PE-AAs) with different amounts of acrylic acid but exhibiting similar rheological properties were studied to investigate the effect of acrylic acid content in PE-AAs on the morphology and mechanical properties of PE-AA/polystyrene (PS) blend compatibilized by poly(styrene-ran-glycidyl methacrylate) (PS-GMA). From morphological observations, there appears to be an optimum amount of acrylic acid in PE-AA that effectively reduces the dispersed domain size in PE-AA/PS blend systems. The existence of an optimum value is due to the combined effects of a sufficient reaction near the interface giving enough amounts of graft copolymers as a compatibilizer between PE-AA and PS, and fast diffusion of reactive species toward;he interface. However, the tensile strength (sigma(b)) and the elongation at break (epsilon(b)) for these blend systems steadily increased with an increase in the amount of acrylic acid in PE-AA. By increasing the amount of PS-GMA, sigma(b) and epsilon(b) for all blend systems increased rapidly, and then levelled off. Impact strength of these blend systems was investigated by varying them amount of acrylic acid in PE-AA.