The oxalate co-precipitation method was employed to synthesize nanocrystalline Ba0.4Sr0.6TiO3 having an average particle size of 100 nm. The conventional sintering (CS) and spark plasma sintering (SPS) methods were used to fabricate Ba0.4Sr0.6TiO3 ceramics with different microstructures. The SPS sample presented uniformly dense microstructure and ultrafine grains, while abnormal grain growth and some pores were discerned in the CS sample. The differences in microstructure significantly affected the dielectric properties and energy storage performance of the ceramics. The dielectric constant of the SPS sample was high (epsilon' (similar to)1200), its dielectric loss was low (tan delta (similar to)0.003), and the sample presented diffuse phase transition and high breakdown strength (E-b = 260 kV/cm) at room temperature. Compared with the CS sample, the maximum energy storage density and energy storage efficiency of the SPS sample were increased from 0.61 to 1.20 J/cm(3) and 72.6% to 91.6%, respectively. All results revealed that SPS is a powerful technique to produce dense ceramics with high energy storage performance.