The effects of compatibilizing agents on the morphology and properties of high density polyethylene (HDPE) and polyamide-6 blends were investigated. The ternary blends were studied with the objective of understanding and optimizing the compatibilization of HDPE and polyamide-6. The blends were prepared by melt mixing the individual components in a twin-screw extruder. Mechanical property, theological property, differential scanning calorimetry, and scanning electron microscopy results are discussed. The addition of compatibilizing agents results in a greatly reduced dispersed phase particle size. The properties of the blends level out after a compatibilizer level of 3 wt% has been reached. The theological, mechanical, and thermal property results indicate the presence of the compatibilizing agent along the interfacial boundary regions between the other two phases.