The title Schiff base compound, C(13)H(11)N(3)O(5)S, exists in an E configuration with respect to the C=N double bond. The benzene rings are almost coplanar, making a dihedral angle of 2.82 (6). The sulfonamide group is twisted away from the attached phenyl ring with an N-S-C-C torsion angle of 64.84 (11)°. An intra-molecular O-H⋯N hydrogen bond stabilizes the mol-ecule, generating an S(6) ring motif. In the crystal, inter-molecular N-H⋯O and C-H⋯O hydrogen bonds link the mol-ecules into a three-dimensional network.