Glass-ceramics in the BaO-Na2O-Nb2O5-SiO2system were fabricated by a controlled-crystallization process. During the process, different heat treatment conditions were applied. Phase formation, micro-structural arrangement, and dielectric properties of the glass-ceramics were investigated by XRD, SEM, and Dielectric spectroscopy techniques. The results of phase identification revealed that NaNbO3(NN) with perovskite crystals formed at a treatment temperature close to the crystallization peak (Tcr) which was suggested by DTA study of the parent glass. At a higher treatment temperature, Ba3Nb6Si4O26(BNS) with layered structure was found as the additional crystalline phase. Both crystalline phases distributed randomly throughout the whole bulk glass-ceramic specimens with no observation of phase clustering. The plots of dielectric constant versus temperature revealed the dielectric response of the ferroelectric NaNbO3crystals. With the presence of Ba3Nb6Si4O26phase, there was no pronounced effect on the phase transition of the NaNbO3but it enhanced the dielectric constant at Tmax. The dielectric spectroscopic investigation revealed that dipolar polarization is responsible for overall dielectric contribution. [ABSTRACT FROM AUTHOR]