In the structure of the title salt, C12H10N 3O4+·C7H3N 2O7-, the cations and the anions are linked by a single N+ - H⋯Ocarbox-yl hydrogen bond, the discrete cation-anion unit having no inter-molecular associations other than weak cation-anion aromatic ring π-π inter-actions [ring centroid separation = 3.7320 (14) Å] and a number of weak inter-unit aromatic C - H⋯O contacts. An intramolecular C - H⋯O hydrox-yl-carboxyl hydrogen bond occurs in the anion.