(1-2x)(Ba_0.8Sr_0.2)TiO₃-x(Bi(Mg_0.5Ti_0.5)O₃-NaNbO₃) (x = 0 - 0.33) ceramics were prepared by solid-state synthesis and the dielectric properties were investigated. At x = 0, the ceramics showed a ferroelectric behavior, and thus the dielectric properties were strongly dependent on electric field and temperature. With increasing x, the ferroelectric behavior became weak, and the electric field and temperature dependence became smaller. For the ceramics with x = 0.25 and 0.33, the dc bias and temperature dependence of the dielectric constant was small, that is, the dielectric constant was 310 – 573 under dc bias fields of 0 - 180 kV/cm and temperatures of 25 - 400 ˚C. Moreover, at x = 0.33, the grain size dependence was also small; the dielectric constant at 25 ˚C and no dc bias was 481 – 561 at grains sizes of 1.0 – 3.2 μm. These stable dielectric properties indicated that the ceramics could be candidate materials for high temperature, dc-bias-free capacitor applications.