In the title compound, C(7)H(7)N(2)S(+).C(4)H(5)O(5)(-), the ions are connected by N-H...O hydrogen bonds. The hydrogen oxydiacetate residues are linked together by O-H...O hydrogen bonds disordered about centres of inversion into hydrogen-bonded ribbon layers crosslinked by weak C-H...O and stacking interactions. The cation exists mainly in the 2,3-dihydro-1,3-benzothiazol-2-iminium form, with a small participation of the 2-aminobenzothiazolium form, based on the structural data and quantum mechanical calculations. This study provides structural insights relevant to the biochemical activity of benzothiazole molecules.