In the title compound, C(4)H(4)N(2)O(2), both imidazole N atoms are protonated and carboxyl-ate group is deprotonated, resulting in a zwitterion. The mol-ecule is essentially planar, with an r.m.s. deviation of 0.012 (1) Å. In the crystal, N-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distance = 3.674 (2) Å] between the imidazole rings link the mol-ecules into a three-dimensional supra-molecular network.