Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, silicon and silicide defects in nitrogen-rich La-Si-O-N glasses were investigated. Glasses were prepared by heating powder mixture of La metal, Si 3 N 4 , and SiO 2 in a nitrogen atmosphere at 1650-1800°C. The obtained glasses containing an unprecedented amount of N content of up to 68 e/o and La up to 62 e/o in the glass network which reveals a broader glass-forming region in the system than previously reported. The microstructure and impurities in the glasses were examined by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in conjunction with electron energy-loss spectroscopy (EELS). Analyses showed that the glasses contain a small amount of spherical La silicides particles, mostly amorphous or poorly crystalline, and having sizes typically ranging from 1 µm and less. The amount of silicide was estimated to be less than 2 vol.%. There was no systematic relation between silicide formation and glass composition or preparation temperature, but it was found that particle size decrease with increasing holding time. The limited transparency of high N-containing glasses is expected to have attribution of elemental Si and microscopy analyses, and Raman spectroscopy ascertained silicide particles. Furthermore, a metallic silicide formed by the decomposition of silicon oxide and silicon nitride, then the subsequent reaction of Si and La.