Heteroatomic high-spin molecules are suitable for a model study of room-temperature stable molecular based magnetics. We studied high-spin nitrenes (S = 1 and 2) with s-triazine skeleton, which were generated by the photolysis of the polyazide precursor. We identified mononitrene 1 (S = 1) and bisnitrene 2 (S = 2) for the first time by single-crystal ESR measurements. The fine-structure parameters were determined by the angular dependence of resonance fields. The determined fine-structure parameters were \D\ = 1.402 cm(-1) and \D\ = 0.280 cm(-1) for mononitrene 1 and bisnitrene 2, respectively. The large D values indicate that pi -spin delocalization effects were hampered by introducing heteroatoms to pi -spin systems. The hyperfine splittings due to the monovalent nitrogen nucleus of 1 were observed with magnetic field along the principal axis of the fine structure tensor. The hyperfine splitting constant was about 0.0018 cm(-1). The temperature dependence of ESR signals showed that 1 and 2 were triplet and quintet in the ground state, respectively.