The structure, mechanical and electrical properties of melt mixed HDPE/MWCNT composites processed by compression moulding and blown film extrusion were investigated in this study. The addition of MWCNTs leads to a more uniform thickness distribution of the blown films due to the deformation of the material being more stable in film blowing. Compared with the compression moulded composites, the blown composite films exhibit enhanced mechanical properties due to the orientation and disentanglement of MWCNTs. At a blow up ratio (BUR) of 3, the breaking strength and elongation in the machine direction of the blown film with 4 wt% MWCNTs are respectively 239% and 1054% higher than those of compression moulded samples. The compression moulded composite containing only 2 wt% MWCNTs exhibits a great decrease of 13 orders of magnitude in resistivity relative to the pure HDPE sheet, indicating the formation of lots of conductive pathways. However, the resistivity of the composite films increases significantly with increasing BURs due to the destruction of conductive pathways. There is no significant increase in the resistivity of the composite films containing 8 wt% MWCNTs due to a sufficient density of nanotubes forming a robust conductive network.