Abstract: The microstructure of Si₃N₄ with non-toxic, non-oxide additive consisting of ZrN and A1N was examined by TEM and EDS. Minor intergranular glassy phase is observed at few triple regions, but is not found in most of grain boundaries in this new Si₃N₄-based ceramics. The superior HT properties are attributed to the significantly reduced amount of intergranular glassy phase and increase of its softening temperature. Many ZrN particles dispersed in matrix and secondary crystalline phase distributed in triple regions of grain boundaries are observed. Superior mechanical properties are closely related to the micro-structure features. In addition, different superstructures in α'-Si₃N₄ are found by lattice imaging.