High density polyethylene (HDPE), calcium carbonate (CaCO3), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (T (m)) and the crystallization temperature (T (C)) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO3 was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO3, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G') with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO(3) blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO3 with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO3 by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO3/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.