The current study is to investigate the influence of inserting chemically modified titanium oxide (TiO 2 ) nanoparticles on the dielectric and mechanical properties of the commercial compound Polyvinyl Chloride (PVC) used in insulating power cables. The surface modification of TiO 2 nanoparticles was performed using vinyl silane coupling agent after activating their surfaces with methane-sulfonic acid. The PVC pellets were first dissolved using suitable solvent. Then, PVC/TiO 2 nanocomposites, with different loadings of nanoparticles, were synthesized with the aid of ultra-sonication for better dispersion of nanoparticles. The morphology of the prepared nanocomposites was studied by field emission scanning electron microscopy (FE-SEM), and their mechanical properties were studied by performing tensile test at speed of 50 mm/min. The results showed that the insertion of functionalized nanoparticles is able to increase the tensile strength and the Young's modulus of the prepared samples, however it decreases their elongation. The dielectric properties, such as dielectric constant and dielectric loss, were also studied in a range of frequencies between 20 Hz and 1 MHz. Moreover, AC breakdown voltage of prepared samples was measured under uniform and semi-uniform field, and then, AC dielectric strength was evaluated using Finite Element Method (FEM) for semi-uniform field. For further evaluation, DC breakdown voltage was also measured under uniform field. PVC/TiO 2 nanocomposites with functionalized TiO 2 exhibited better dielectric properties compared to that with un-functionalized TiO 2 or that of base PVC. This may be attributed to the low surface energy of the functionalized TiO 2 nanoparticles that prevented the agglomeration of nanoparticles and restricted the mobility of polymeric chains.