[en] The possible crystal structures of transition metal nitrides M₂N₃ (M = V or Nb) were investigated using first principles calculations. We predict that the ground state structures of V₂N₃ and Nb₂N₃ are trigonal and orthorhombic, respectively, over a wide pressure range. Examinations of the thermodynamic stabilities of trigonal V₂N₃ and orthorhombic Nb₂N₃ with respect to phase decomposition suggest that they can be prepared under moderate pressure conditions. Elastic constant calculations indicated that both nitrides were mechanically stable and are potential candidates for hard materials.