Structures of a series of silylnitrenes formed from silyl azides were investigated by means of ESR. gamma -Irradiation and photo-illumination of all the silyl azides resulted in the formation of triplet states even for those having two or three Si-N-3 groups in a molecule. ESR spectra of the silylnitrenes exhibited a part of the fine structure at around 820 mT. All the silyl azides studied gave nearly identical D-values (ca. 1.5 cm(-1)) and much larger than those in phenylnitrenes. The results suggested that electron spins are localized in the nitrogen p-orbitals to a large extent and was interpreted in terms of a mono-silane linkage of nitrene, -Si-N:, i.e., interrupting spin delocalization.