It has been shown that the band gap engineering plays vital role in the designing of new semiconductors. Therefore, many research groups have focused on various techniques to tune the band gap such as chemical doping and strain energy. In the present work, polycrystalline YbFeO3-delta (YbFO) and YbFe1-xCoxO3-delta (YbFCO) (x = 0.01 and 0.10) thin films were grown on indium tin oxide (ITO) substrates at 500 degrees C by magnetron sputtering technique. The crystalline orientation of the thin films has been studied by XRD. SEM and AFM have been utilized in the surface topographical investigations and XPS analysis was carried out in order to reveal the oxidation states of elements in studied materials. It has been shown that the optical band gap YbFO can be tuned from 2.1 eV to 1.72 eV via Co doping into Fe sites. Furthermore, diffuse reflectance spectroscopy (DRS) has been employed to study reflectance %, refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constant and conductivity.