The structure and dielectric properties of bulk ceramics in the xCa2AlNbO6: (1-x)Ca3Nb2O8 system were studied. Ca₂AlNbO₆ (P21/n, a = 5.3785(1) Å, b = 5.4158(1) Å, c = 7.6259(1) Å, b = 89.93(1)^o) is a double perovskite with structure similar to CaTiO₃ and Ca₃Nb₂O₈ is a defect perovskite-related phase (a = 23.803(1) Å).  The end members exhibit temperature coefficients of resonant frequency (Df) that are opposite in sign; therefore, compositions along the tie line between them were prepared to examine the dielectric properties.  Materials in this system exhibit modest relative permittivities (24 < e_r < 39) and low dielectric loss (7000 < Q x f < 14000 at 6 GHz). At the composition near x = 0.6, the relative permittivity is 26 with Df near 0 ppm at 7 GHz. Synthesis, structural characterization from single-crystal X-ray and powder neutron diffraction, and the dielectric properties of the phases will be described.