The high-voltage electrical porcelain insulator plays an important role in the electrical power industry. The effect of silica nanoparticles (NS) addition on the electrical and physical properties of porcelain insulators sintered at different temperatures was investigated in the present study. Kaolin, feldspar, and quartz (in the form of silica sand) were used as economical raw materials to prepare porcelain insulator samples. Different additions of silica nanoparticles (0–15 wt%) were used. The porcelain specimens were compressed under 50 MPa pressure and treated at different sintering temperature (from 1100 to 1400 °C). The morphology and microstructure of the raw materials and some selected specimens were investigated using scanning electron microscope. Phase composition of some selected samples was identified using X-ray diffraction, to evaluate the thermal, structural, and microstructural changes by increasing the concentration of silica (0–15 wt%). The dielectric properties were evaluated by measuring the AC breakdown strength, the relative permittivity (εr) and dielectric loss (tan δ) at different frequencies at room temperature. A finite element method axi-symmetrical model of the samples with the help of FEMM 4.2 package is used to evaluate their breakdown strength. The results revealed that the physical and dielectric properties of porcelain samples enhanced by increasing the sintering temperature. The porcelain samples admixed with 10 wt% silica nanoparticles and sintered at 1300 °C present the maximal density (3.57 g/cm3), minimal water absorption (0.0173%) and minimal porosity values (0.043%) as well as a good insulating characteristic.