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The zwitterionic title compound, C16H12N2O3, was obtained as a result of the condensation of 5-aminosalicylic acid and 1H-indole-3-carbaldehyde. The whole molecule is roughly planar: the 4-hydroxyanilinic group and the 1H-indole-3-carbaldehyde moieties are only slightly twisted, making a dihedral angle of 7.77 (11)°, whereas, the carboxylate group makes a dihedral angle of 3.34 (45)° with the parent 4-hydroxyanilinic group. S(6) ring motifs are formed due to intramolecular O—H...O hydrogen bonding. In the crystal, intermolecular N—H...O and C—H...O hydrogen bonds build up pseudo-rings with R12(4), R21(7) and R22(14) ring motifs. These pseudo-dimers are further linked by N—H...O hydrogen bonds into a chain extending along [101]. C—H...π interactions also occur, along with offset π–π interactions between the anilinic phenyl and the heterocyclic five-membered rings with a centroid–centroid distance of 3.5716 (19) Å.