The title compound, C 6 H 8 N 2 O 4 , a new derivative of isoxazole, has been synthesized and structurally characterized. crystal structure shows the molecule to be almost planar (r.m.s. deviation for non-hydrogen atoms = 0.029 Å), this conformation being supported by an intramolecular N—H...O hydrogen bond. In extended structure, molecules are linked bonds into chains propagating along [010].