In the title mol-ecule, C(17)H(16)N(2)O(4)S, the heterocyclic thia-zine ring adopts a half-chair conformation, with the S and N atoms displaced by 0.546 (4) and 0.281 (4) Å, respectively, on opposite sides of the mean plane formed by the remaining ring atoms. The mol-ecular structure is stabilized by an intra-molecular O-H⋯O hydrogen bond. The two aromatic rings are inclined to one another by 42.32 (11)°. In the crystal, mol-ecules are linked by pairs of N-H⋯O hydrogen bonds, forming inversion dimers. The dimers are linked via a series of C-H⋯O inter-actions, leading to the formation of a three-dimensional network.