Sintering of titanium oxynitride, TiOxNy (x+y≈1, x=0.07-1.00, y=0-0.89) was studied at 1000°-1400°C. The rate of sintering decreased markedly with increasing nitrogen content, y. The results were tentatively analyzed with an initial stage sintering equation. The diffusion coefficient of rate limiting species of sintering changes four orders of magnitude for TiO in which -90% of oxygen was substituted with nitrogen. The relation between the defect concentration and the diffusion coefficient of rate limiting species of sintering was discussed.