Graft copolymerization of high density polyethylene with a maleic anhydride was carried out using intermeshing co-rotating twin screw extruder in the presence of benzoyl peroxide (BPO).The HDPE/PA6 and HDPE-g-MAH/PA6 blends were prepared in a co-rotating twin screw extruder. The melt viscosity of the grafted HDPE was measured by a capillary rheometer. The grafted copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microcopy (SEM). The influence of the variation in temperature, benzoyl peroxide (BPO) and maleic anhydride (MAH) concentration and temperature on the grafting degree and on the melt viscosity were studied. The grafting degree increased appreciably up to about 0.4 phr, and then decreased continuously with an increasing BPO concentration. Furthermore, the results revealed that the tensile strength of the blends increases linearly with increasing polyamide 6 content. The results of scanning electron microcopy (SEM) and mechanical test showed that the blends have good interfacial adhesion and good stability of the phase structure, which is reflected in the mechanical properties.