The perovskite-type oxynitride SrTaO2N was synthesized from Sr2Ta2O7 and carbon nitride (C3N4) and the formation mechanism was investigated using X-ray diffraction and thermogravimetry combined with mass spectrometry. In this process, ammonia is not required for the nitridation of the oxide. The C3N4 thermally decomposes to gaseous C2N2, which forms SrCN2 and Ta3N5 intermediates on the Sr2Ta2O7. These intermediates then react with the oxide to form SrTaO2N at 800 degrees C, which is 200 degrees C lower than the temperature required for the ammonolysis of Sr2Ta2O7. The product was SrTaO2N, having a slight nitrogen deficiency and small particle size because the present C3N4 nitridation was performed at lower temperature than conventional ammonolysis.