Surface modification of high-density polyethylene (HDPE) surfaces by plasma polymerization of glycidyl methacrylate (GMA) (the pp-GMA-HDPE surfaces), in the absence and presence of Ar plasma pre-activation of the HDPE substrates, was carried out to enhance the adhesion of the polymer with evaporated copper. The FTIR and X-ray photoelectron spectroscopy (XPS) results suggested that the epoxide functional groups on the pp-GMA-HDPE surfaces had been preserved to various extents, depending on the RF power used during plasma polymerization. Ar plasma pre-activation of the HDPE surface led to the strong interaction of the pp-GMA layer with the HDPE substrate. GMA plasma polymerization at low RF powers and in the presence of Ar plasma pre-activation was shown to be an effective method for enhancing the adhesion of HDPE with the evaporated Cu. An optimum adhesion strength of about 16 N/cm was achieved between the evaporated Cu and the pp-GMA-HDPE surface prepared by plasma polymerization of GMA at 5 W, 100 Pa, 20 sccm for 5 s on the HDPE surface pre-activated by Ar plasma at 35 W, 100 Pa 20 sccm. for 20 s. The adhesion enhancement of the Cu/pp-GMA-HDPE assemblies in the presence of Ar plasma pre-activation of the HDPE substrate was attributed to the covalent bonding of the plasma-polymerized GMA (pp-GMA) layer with the HDPE surface, the preservation of the epoxide functional groups in the pp-GMA layer, and the spatial interactions of pp-GMA chains with the evaporated Cu matrix.