Zinc oxy fluoro borate glasses mixed with different concentrations of CoO (ranging from 0 to 2.0mol%) are synthesized and subsequently crystallized. The scanning electron microscopy pictures have exhibited crystallinity. Differential scanning calorimetric studies have indicated that the prepared samples consist of multiple crystal phases. The X-ray diffraction patterns have indicated that the glass-ceramic samples are composed of Zn(BO2)(2,) (Zn)(3)(BO3)(2,) CoF2, CoF3, Co3FB7O13, ZnCo2O4, Co3O4 crystalline phases. The optical absorption and photoluminescence studies have indicated that there is a gradual increase of tetrahedral cobalt ion concentration with increase of CoO concentration in the glass network. IR spectroscopic studies have pointed out increased degree of polymerization of the zinc oxy fluoro borate glass network with increase of CoO content. The analysis of results of dielectric properties indicated increase of insulating strength of the glass-ceramics with increase of CoO content. Finally, the dielectric breakdown strength of the samples is measured at room temperature in air medium and it is found to increase from 12.9 to 19.2kV/cm with increase of CoO from 0.2 to 2.0mol%. The reasons for such increase of breakdown strength are discussed quantitatively in terms of dielectric parameters with aid of data on spectroscopic properties.