Dielectric capacitors with high capacitive energy storage are urgently needed to meet the growing demand for high-performance energy storage devices. Herein, a novel lead-free Sr5BiTi3Nb7O30(SBTN) tungsten bronze relaxor ferroelectric ceramic is prepared and explored for potential energy storage applications. A high recoverable energy density Wrec(∼3.72 J/cm3) and ultrahigh efficiency η(∼94.2%) at 380 kV/cm are achieved simultaneously. Both Wrecand ηexhibit superior stabilities against temperature (30–140∘C), cycles (100–105) and frequency (1–500 Hz). In addition, a high current density of 796 A/cm2and a large power density of 71.7 MW/cm3are achieved, together with good thermal endurance and fatigue resistance. These results demonstrate that the obtained SBTN ceramic can be deemed as the promising candidates for dielectric capacitor applications.