Two-step crystallization process was employed to improve microstructure and energy-storage density of the strontium barium niobate-based/titanate-based glass-ceramics. By using two-step crystallization process, the optimum nucleation temperature was obtained to improve dielectric breakdown strength. Compared to the breakdown strength by one-step crystallization process, the breakdown strength by two-step crystallization process is increased about 1.89 times with the optimum nucleation temperature. Energy-storage density of 7.73 +/- 0.26J/cm(3) is significantly improved by two-step crystallization process and is about 2.9 times of 2.63 +/- 0.17J/cm(3) by one-step crystallization process. This result is attributed to the homogeneous nucleation improving the microstructures of glass-ceramics. Identification and quantification of crystalline phases by using Rietveld refinement reveals the difference of dielectric constants for one-step and two-step crystallization processes.