Strontium barium niobate-based glass-ceramics are prepared by melt-casting followed by controlled crystallization. Results show that Ba0.25Sr0.75Nb2O6 with tungsten bronze structure forms as the dielectric phases from the glass matrix at 800°C. However, a secondary phase NaSr1.2Ba0.8Nb5O15 occurrs when crystallization temperature exceeds 850°C. The glass-ceramics formed through controlled crystallization exhibit the excellent stability of the temperature and frequency dependence of dielectric properties. The breakdown strength increases with the crystallization temperature. The glass-ceramic material heated at 800°C/3h+950°C/3h shows a breakdown strength of 1400 kV/cm and its energy storage density can reach up to 4.0 J/cm3, which may be strong candidate for high energy density storage capacitors for portable or pulsed power applications.