The title compound, C(13)H(10)N(+)·C(7)H(4)NO(4) (-), consists of a protonated acridinium cation and a 6-carb-oxy-pyridine-2-carboxyl-ate monoanion. The carboxyl-ate group of the anion appears to be delocalized on the basis of the nearly equivalent C-O bond lengths. In the crystal, the anions are connected by strong O-H⋯O hydrogen bonds, forming chains along the b axis. The acridinium cations are linked to the anionic chains by strong N-H⋯O hydrogen bonds between the carboxyl-ate group of the anion and the N-H group of the cation. Along the b axis, successive chains stack in opposite directions. Weak inter-molecular C-H⋯O hydrogen bonds further stabilize the crystal structure.