Microfibrillar composites from high-density polyethylene (HDPE-75 wt%) and polyamide-6 (PA6-25 wt%) were made through a reactive extrusion at the processing temperature of PA6 in combination with hot stretching to form microfibrillar composites, and injection molding at the melt temperature of HDPE to form final composites. The scanning electron microscope observations demonstrated the formation of the PA6 microfibers during extrusion. Incorporation of PA6 microfibers led to an improvement in both flexural and tensile properties as compared to the neat HDPE. Use of ethylene-glycidyl methacrylate copolymers (E-GMA) in the composites gave the highest tensile modulus, while ethylene, butyl acrylate and maleic anhydride terpolymer (E-BA-MA) led to the highest tensile strength and elongation. The maleic anhydride grafted polyethylene (MAPE) was the most efficient among three coupling agents in improving impact strength. With the addition of 5 wt% E-GMA, E-BA-MA and MAPE, the HDPE/PA6 composites exhibited an improvement of 87, 116, and 387 %, respectively, compared to the uncoupled controls. The PA6 microfibers exhibited a regular orientation along the stretching direction in the presence of 2.5 wt% coupling agents; increasing the loading level of coupling agents caused a reduction in the diameter of PA6 microfibers. FT-IR analyses showed the reactions between PA6 and the coupling agents used.