Abstract: A hydrothermal precipitation technique was used to synthesize TiO2 oxide nanoparticles doped with Bi/ Ni ions. X-ray difraction, difuse refection spectroscopy, and ac-dielectric measurements were used to investigate the mechanical, optical, and dielectric properties of the synthesized NPs powder. Using Bi/Ni ionic codoping, TiO2 NCs were constructed as core/shell nanostructures. A key contribution of this work was the creation of colossal permittivity (CP). Thus, the dielectric measurements show CP of magnitude ~ 5× 106 at room temperature and frequency of 1 kHz that was reduced to 2.7× 105 by the hydrogenation of the sample, which are much more than that of pristine TiO2. Within the framework of the core/shell model and doping mechanisms, CP was explained in detail. Additionally, hydrogenation was explained as a reduction in CP by increasing itinerant electron concentrations as a result of the strong catalyst power of dopant Ni2+ ions dissociating adsorbed hydrogen.