A reactive compatibilizer, styrene-maleic anhydride (SMA) was used to compatibilize the blends of polystyrene (PS) and ethylene-vinyl acetate-vinyl alcohol (EVAOH), which was synthesized from ethylene-vinyl acetate (EVA) using transesterification reaction. The compatibilized blends with different compositions were prepared using a twin-screw extruder and injection molded into the required test specimens. Morphology of Charpy impact-fractured surfaces, tensile, and impact properties of the blends were investigated. Fourier-transform infrared spectroscopy (FTIR) was also applied for specific samples to elucidate the presence of the functional groups reaction necessary for reactive compatibilization. The results of the ternary PS/EVAOH/SMA blends illustrate that the addition of SMA as a compatibilizer slightly reduce the elongation at break. From the impact-fractured surfaces of the blends, it is evident that the morphology developed sizable pores when SMA was added into the blends. This might be attributed to the residual octanol-1, produced from the synthesis of EVAOH, as there is a possibility of a reaction between hydroxyl groups in the octanol-1 and the anhydride groups in the SMA. This disrupted the stability of the morphology and resulted in the decrease in the elongation, and hence, the tensile toughness.