This study aimed to investigate the optical, electric and dielectric properties of the Ni0.5Co0.5-xCdxNd0.02Fe1.78O4 (x <= 0.25) NFs prepared via electrospinning process. Diffuse reflectance spectroscopic (DRS) measurements were performed on pristine and all Cd-substituted NFs samples. Direct bandgap energies (E-g) were extracted from the Tauc fits which were estimated in a range between 1.65 and 1.85eV. The electrical conduction mechanism and dielectric functions of Ni0.5Co0.5-xCdxNd0.02Fe1.78O4 NFs were comprehensively examined as functions of frequency, temperature and Cd ions substitution ratio in a 3D semi-logarithmic plot using the complex impedance spectroscopy technique. The substitution ratio has a robust influence on dielectric parameters including dielectric loss, dielectric constant, and dissipation factor while the Cd ion substitution has a weak effect on the conductivity mechanism. The activation energy values changed to a level lower than 400 meV with increasing the "x" values.