The title compound, also known as 7-nitro-tropolone, C7H5NO4, exists in the crystalline state as the 2-hy-droxy-7-nitro-cyclo-hepta-2,4,6-trien-1-one tautomer and not as 2-hy-droxy-3-nitro-cyclo-hepta-2,4,6-trien-1-one. The dihedral angle between the ring and the nitro group is 70.3 (2)°. In the crystal, neighbouring mol-ecules are linked into dimers by a pair of O-H⋯O hydrogen bonds. In addition, the crystal is stabilized by O⋯π [3.4039 (14) Å] and O⋯O [3.073 (2) Å] inter-actions.