Ceramics in the solid solution system, (1-x)Ba0.8Ca0.2TiO3-xBi(Mg0.5Ti0.5)O3, were prepared by a conventional mixed oxide route. Single-phase perovskite-type X-ray diffraction patterns were observed for compositions x<0.6. A change from tetragonal to single-phase cubic X-ray patterns occurred at x0.1. Dielectric measurements indicated relaxor behavior for x0.1. Increasing the Bi(Mg0.5Ti0.5)O3 content improved the temperature sensitivity of relative permittivity Er at high temperatures. At x=0.5, a near-plateau relative permittivity, 835 +/- 40, extended across the temperature range, 65 degrees C-550 degrees C; the permittivity increased at x=0.6 to 2170 +/- 100 for temperatures 160 degrees C-400 degrees C (1kHz). The corresponding loss tangent, tan, was 0.025 for temperatures between 100 degrees C and 430 degrees C for composition x=0.5; at x=0.6, losses increased sharply at >300 degrees C. Comparisons of dielectric properties with other materials proposed for high-temperature capacitor applications suggest that (1-x)Ba0.8Ca0.2TiO3-xBi(Mg0.5Ti0.5)O3 ceramics are a promising base material for further development.