A novel niobium nitride, U2S3-Type Nb2N3, has been successfully synthesized by nitridation of delta-NbN above approximately 30 GPa in a laser-heated diamond anvil cell. Nb2N3 crystallizes in the same orthorhombic structure (space group: Pnma) as eta-Ta2N3. Nb2N3 consists of regular-shaped polyhedra, and the bulk modulus has been determined to K-0 = 300(2) GPa. The low-temperature X-ray diffraction measurements have been successfully conducted for the tiny novel Nb2N3 between 297.7(5) and 106.3(3) K under ambient pressure. Nb2N3 shows no structural phase transition down to 106.3(3) K, and investigation of the linear thermal expansion coefficients yields alpha(a) = 3.36(9) x 10(-6) K-1, alpha(b) = 5.39(10) X 10(-6) K-1 , alpha(c) = 6.77(15) X 10(-6) K-1, respectively. Our study reveals that the incompressible novel nitride shows low thermal expansion behavior, which offers new insights for the development of functional nitrides and their crystal chemistry.