ABSTRACT : Fe/Nb and Co/Nb co-doped TiO2 ceramics were synthesized by conventional ceramic solid-state reaction process in order to create a high dielectric permittivity substance. Comprehensive structural, optical and dielectric studies were carried out on the samples of formula Nb:TiO2, Fe:(TiO2 :Nb) and Co:(TiO2 :Nb). The structural and optical characterizations were performed with X-ray diffraction and diffuse reflection spectroscopy, respectively. The dielectric properties including colossal permittivity (CP) were investigated at room temperature in the frequency range of 0.1-100 kHz. The novelty of the present work was to create a CP (~104-105) in host TiO2 by cod oping with (Co/Nb) and study the change in the CP by using Fe ions instead of Co ions. The results were explained in the framework of the core/shell model and doping mechanisms.