In the title compound (systematic name: 2,3-dimethoxy-10-oxostrychnidinium 2-carboxy-6-nitrophthalate dihydrate), C23H27N2O4+烸H4NO6-粈2O, the carboxylic acid and carboxylate groups of the hydrogenphthalate anions form head-to-tail catemeric chains of strong intermolecular O-HO hydrogen bonds [OO distance = 2.563 (5) ŝ along the 21 screw axes parallel to the a axis. The chains further associate with the water molecules, forming sheet structures parallel to (010). The protonated N atom at the 19-position of the brucine molecule forms a peripheral intermolecular hydrogen bond with the carboxylate group of the anion.