The maintaining of the chemical composition and electrical insulativity of SrTaO 2 N ceramics was investigated during sintering and annealing, using powders prepared by the nitridation of Sr 2 Ta 2 O 7 . Due to the low thermal stability of SrTaO 2 N, the partial loss of SrO and nitrogen induced the formation of a TaO 0.9 impurity after heat-treating at above 1100°C. The sintering additive SrCO 3 and postannealing in NH 3 were employed to compensate for the loss of SrO and nitrogen to obtain ceramics with the original chemical composition. The as-sintered SrTaO 2 N ceramics with various relative density (RD) were annealed in NH 3 to observe the recovery of color and electrical insulativity. It was found that the inner part of the well-sintered samples with RD = 95.1% could not be recovered by annealing, and continued to exhibit semiconducting behavior and a black color. On the other hand, for the as-sintered SrTaO 2 N ceramics with RD < 84%, both the nitrogen content and electrically insulating behavior were completely recovered after annealing. The postannealed SrTaO 2 N ceramics (RD = 83.3%) possessed a relatively large dielectric constant of 450 with a low dielectric loss of less than 0.1 at 100 Hz, almost independent of frequency and temperature.