There are two mol-ecules in the asymmetric unit of the title compound, C(15)H(11)NO(4)S. The heterocyclic thia-zine rings in both mol-ecules adopt half-chair conformations with the S and N atoms displaced by 0.455 (4) and 0.254 (4) Å, respectively, in one mol-ecule, and 0.480 (4) and 0.224 (5) Å in the other, on opposite sides of the mean planes formed by the remaining ring atoms. The crystal structure is stabilized by inter-molecular N-H⋯O and C-H⋯O hydrogen bonds. In addition, intra-molecular O-H⋯O inter-actions are also present.