Currently, several deep-rooted researches have focused on the significance and application of polymers in electrical and mechanical fields. This is because of the benefits of polymers in its availability, recyclability, and flexibility in processing; economical and most importantly improvement in material property have been achieved by incorporating nanosized metal oxide (inorganic) additives in the polymer matrix. In this study, HDPE (High Density Polyethylene) is considered as base polymer and alumina as nanoadditive. Alumina (Al2O3) nanofillers are incorporated in HDPE as 1 wt.%, 3 wt.%, 5 wt.%, and 7 wt.% filler compositions. From the dielectric analysis, it has been inferred that HDPE with 3 wt.% nanoalumina achieved higher permittivity compared with other samples. Also, 5 wt.% composite samples has gained 18.46% improvement in inception voltage, 16.3% increase in the breakdown strength, and 94.47% enhanced thermal conductivity compared with pure HDPE.