The dispersion of starch as a filler in hydrophobic ethylene-co-vinyl acetate (EVA) rubber is an issue. To obtain a fine dispersion of starch in EVA rubber, EVA/starch blends were prepared by reactive extrusion in the presence of maleic anhydride (MA), benzoyl peroxide (BPO), and glycerol. MA, BPO, and glycerol play the role of coupling agent, free-radical initiator, and plasticizer, respectively. Molau experiment and Fourier transform infrared spectroscopy (FTIR) results showed that EVA chains were grafted onto the surface of starch particles during reactive extrusion via a free-radical grafting mechanism. As a result, EVA-g-starch copolymers acted as a compatibilizer, leading to fine dispersion of starch and strong interfacial adhesion between the starch and the EVA matrix. Scanning electron microscope (SEM) images showed that the starch particle size reduced from hundreds micrometers in the case of physical blending to approximately 1 micrometer in the case of reactive blending, and consequently, the EVA rubber was effectively reinforced by the incorporation of starch and the reactive compatibilization (e.g., the tensile strength of the EVA/starch (50/50, wt/wt) was increased by a factor of 6 after the addition of 0.9-1.8 wt% MA). The property stability of starch compounds is usually an issue, while the mechanical properties of the (compatibilized) EVA/starch blends reported in this article were stable during storage.