Dielectric ceramics with high energy storage density and energy efficiency play an important role in high power energy storage applications. In this work, lead free relaxor ferroelectric ceramics in (1-x)Bi 0.51 Na 0.47 TiO 3 - xBa(Zr 0.3 Ti 0.7 )O 3 (BNT-BZT100x: x = 0.20, 0.30, 0.40 and 0.50) system are fabricated by conventional solid-state sintering method. The BNT-BZT100x ceramics are sintered dense with minimal pores, exhibiting pseudocubic symmetry and strong relaxor characteristic. A high energy storage density of 3.1 J/cm 3 and high energy efficiency of 91% are simultaneously achieved in BNT-BZT40 ceramic with 0.1 mm in thickness, at the applied electric field of 280 kV/cm. The temperature stability of the energy density is studied over temperature range of 20–160 °C, showing minimal variation below 1.5%, together with the excellent cycling reliability (the variations of both energy density and efficiency are below 3% up to 10 6 cycles), making BNT-BZT40 ceramic promising candidate for high-temperature dielectric and energy storage applications.