The glass composition 92.5 Li 2 B 4 O 7 –7.5Nb 2 O 5 (mol%) was prepared by the conventional melt quenching technique. The as-quenched sample, blue and transparent, was heat-treated at 550 and 650 °C (HT). The glassy nature of the as-quenched sample was established by Differential scanning calorimetry (DSC). Lithium niobate LiNbO 3 and Li 2 B 4 O 7 nanocrystals were produced within the glass by heat-treating it at 550 and 650 °C/3. The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Various optical parameters such as optical band gap ( E opt ) and Urbach energy (Δ E ) of these transparent glass–ceramics have been found to be crystallite size dependent. The volume ratio of the particles increases with increase in heat-treatment temperature. The behavior of the σ ac , with the increase in the heat-treatment (HT) temperature, was related with the decrease in the free ions number in the glass matrix and consequent increase in the fraction of the crystallites LiNbO 3 phase to the crystallites Li 2 B 4 O 7 phase and the glass matrix. The dielectric constants of the glass–ceramics decrease with increase in the HT temperature and with increase in frequency (0.12–100 kHz).