The objective of this study is to examine the mechanical, thermal, and physical properties of industrially produced nano-CaCO3 filled high-density polyethylene nanocomposites. For this purpose, 1.0, 3.0, 5.0, 10.0, and 15.0 wt.% loading of nano-CaCO3 filled high-density polyethylene nanocomposites were prepared by the melt mixing method using a compounder system, which consist of industrial banbury mixer, single screw extruder, and granule cutting. The effect of nano-CaCO3 on mechanical, thermal, and physical properties of nano-CaCO3/HDPE nanocomposites was investigated. As a result of all experiments, the tensile strength of nano-CaCO3 filled high-density polyethylene nanocomposite increased about 5% with addition of 1.0 wt.% nano-CaCO3. But did not increase further as more nano-CaCO3 was added. The flexural strength of nano-CaCO3 filled high-density polyethylene nanocomposite increased about 4.5% with addition of 15.0 wt.% nano-CaCO3.Then increased slightly as the nano-CaCO3 content increased to 15.0 wt.%. The tensile and flexural modulus of high-density polyethylene were significantly improved after (from 1.0 wt.% up to 15.0 wt.%) addition of nano-CaCO3. The tensile elongation at break and shore D hardness was consistently decreased with the addition of nano-CaCO3. The nano-CaCO3 filled high-density polyethylene nanocomposites were determined to have lower impact energy level than neat high-density polyethylene. The occurred fracture areas with the impact were detected by scanning electron microscopy examination. It is understood that fracture surface morphology changes when nano-CaCO3 ratio increases. The fracture surface changes were examined to determine the fracture mechanism of nano-CaCO3 filled high-density polyethylene nanocomposites. Density, melting flow index, differential scanning colorimetry, and vicat softening temperature were used to characterize the physical and thermal properties of the nanocomposites. The X-ray diffraction, the fourier transform infrared spectrophotometry, the transmission electron microscopy, and the scanning electron microscopy were used to analyze the structural characteristics of the nanocomposites. It is concluded that the addition of the nano-CaCO3 in high-density polyethylene has significantly influenced the mechanical, thermal, and physical properties of the nanocomposites.