The barium potassium niobate-based glass-ceramics with high energy-storage density, high discharge efficiency, and fast discharge speed have been prepared. It was found that dielectric breakdown strength decreases when the crystallization temperature increases. Glass-ceramics have high energy-storage density up to 14.58 +/- 1.14 J/cm(3) with high breakdown strength of 2382 +/- 92 kV/cm. Discharge energy density and discharge efficiency of glass-ceramic capacitor were achieved through a pulse charge-discharge circuit. The reduction of discharge efficiency with the increase of crystallization temperature is mainly caused by interfacial polarization.