Perovskite-type oxynitrides ACa0.2M0.8O2.6N0.4 (A = Sr, Ba; M = Nb, Ta) were synthesized via the ammonolytic reaction between A5M4O15 and CaCl2, where the Ca2+ insertion and O2−/N3− substitution occurred cooperatively. In terms of the average structure, SrCa0.2Nb0.8O2.6N0.4 and SrCa0.2Ta0.8O2.6N0.4 belong to the orthorhombic Pnma space group, and BaCa0.2Nb0.8O2.6N0.4 and BaCa0.2Ta0.8O2.6N0.4, the primitive cubic Pm3‾m group. The comparison between the experimental lattice volume and the summed ionic volume suggested that ACa0.2M0.8O2.6N0.4 have higher degrees of ionicity than AM'0.2M0.8O3−xNx (M′ = Li, Mg, Mn), but are more covalent than ANa0.2M0.8O2.8N0.2. Despite the significant mismatches of size and charge between Ca2+ and Nb5+ (or Ta5+), no cation ordering was detected on the octahedral site. On the other hand, the O/N distribution appeared to depend on the bonding geometry around the anion sites in a way N favors the straighter bonding connectivity of M−N−M. The band gap energies of ACa0.2M0.8O2.6N0.4 were estimated to be 1.9–2.25 eV depending on A and M. The band gaps and color properties of AMO2N and AM'0.2M0.8O3−xNx (A = Sr, Ba; M = Nb, Ta; M′ = Li, Na, Mg, Ca, Mn) are compared. Thermogravimetry and differential scanning calorimetry were conducted in the air to assess the oxynitride stability. The electrical behaviors were studied by the equivalent circuit analysis of the impedance spectrum using compacted polycrystalline specimens, where BaCa0.2Ta0.8O2.6N0.4 was found to possess a bulk dielectric constant of 4550 along with an electrical conductivity of ≈10−6 S/cm at 27 °C. It remains, however, necessary to assess the extrinsic effects arising from the non-ideal sintering to interpret thoroughly the electrical property of BaCa0.2Ta0.8O2.6N0.4.