High-density polyethylene／elastomer／calcium carbonate ternary composites with dispersed phase of calcium carbonate as a core and maleated elastomer(ethylene—octane copolymer)POEg as a shell were prepared through the reactive extrusion．The improvement of impact strength of HDPE／POEg was limited due to the high miscibility between them．The introduction of CaCO3 had a negative impact on the toushness of the HDPE matrix because of the poor interfacial adhesion．However

in these ternary composites

the calcium carbonate and elastomer showed synergistical toughening effects on the HDPE matrix as a result of the formation of core—shell structures due to the strong interaction between POEg and CaCO3

which improved the HDPE—CaCO3 interfacial strength and the toughness 0f the blends．The brittle-ductile transition occurred at lower contents of POEg for surface treated calcium carbouate based ternary composites compared with the untreated calcium carbonate based ones．