The electrical properties of the polymer/filler composites can be considerably regulated via proper selection of the nanofillers, polymer matrices and appropriate processing conditions. In this study, conductive particle filled polymer nanocomposites were prepared via melt-compounding process. The dielectric and conductive properties of these nanocomposites were systematically investigated. Inorganic nanoparticles such as semiconducting ZnO, noble silver (Ag), self-passivated aluminium (Al), multi-walled carbon nanotube (MWNT) and nanofibers (CNF) were used as conductive fillers for the polymer nanocomposites. Semicrystalline polymers i.e. polypropylene (PP) and polyethylene including low and high density (LDPE and HDPE), and amorphous polystyrene (PS) were selected as the matrices of the nanocomposites. The electrical properties of polymer/filler nanocomposites were greatly dependent on the nature and concentration of fillers used. For the nanofillers with low aspect ratio such as ZnO, Ag and Al, the dielectric constant of the polymer/filler nanocomposites was found to increase almost linearly with an increase of the filler content. No abrupt increase in dielectric constant was observed for the concentration range investigated. The resistivity of the polyethylene/ZnO composites can be satisfactorily described using the interparticle distance approach. The critical interparticle distance for the PE/ZnO composites was determined to be 400 nm. From the interparticle distance concept, we determined a percolation concentration of 52 vol% for the PE/ZnO composites. In the case of nano-Ag filled PP composites, the nanoparticles tended to act as the nucleation sites for PP molecules and to induce the formation of -crystalline form PP. As a result, PP transcrystals formed were adjacent to individual Ag nanoparticles. These insulating PP transcrytals inhibited the formation of conductive pathways in the PP/Ag nanocomposites, thereby degrading their electrical properties. For the fillers with large aspect ratio such as MWNTs or CNFs, the dielectric constant and conductivity of the nanocomposites first increased gradually with an increase of the filler content. As the filler content reached a critical value, a drastic increase in dielectric constant and conductivity occurred, known as the percolation threshold. The critical concentration of the filler was in the range of 0.22-14.3 vol%, depending upon the types of filler and polymer matrix as well as the processing conditions employed. In the presence of MWNTs in PP/Ag composites, the Ag nanoparticles were found to act as anchors for the MWNTs, facilitating the formation of conductive paths in the PP/Ag/MWNT hybrids. In sharp contrast, self-passivated Al particles inhibited the establishment of conductive pathways in the LDPE/Al/MWNT hybrids due to the formation of aluminum oxide. Thus, the hybrids possessed a large percolation concentration. The nature of polymer matrices exerted a significant influence on the dispersion of fillers in polymer matrices. The CNFs were found to disperse uniformly in LDPE and amorphous PS matrices, but agglomerated in HDPE counterpart due to strong crystallizability of HDPE. The different dispersion behavior of CNFs in polymer matrices greatly affected the electrical properties of polymer/CNF nanocomposites. The LDPE/CNF nanocomposites exhibited lower percolation threshold when compared to the HDPE/CNF nanocomposites. The amorphous PS/CNF nanocomposites exhibited the lowest percolation threshold (1.7 vol%) among the samples investigated. Processing conditions also had a pronounced effect on the dispersion of the filler in polymer matrices. Intensive shearing rate favored dispersion of MWNTs in PP matrix, thus enhancing the electrical properties of the composites. The PP/MWNT nanocomposites prepared at a high shearing rate exhibited much lower percolation threshold than that fabricated at a low shearing rate. The conductivity of the polymer/filler nanocomposites near the percolation region was temperature dependent. A sharp increase in resistivity was observed near the transition temperature (melting temperature for semicrystalline polymers and glass transition temperature for amorphous polymers), being associated with the movement of macromolecules of the polymer matrix.