In the title mol-ecule, C(16)H(13)NO(4)S, the heterocyclic thia-zine ring adopts a half-chair conformation with the S and N atoms displaced by 0.410 (3) and 0.299 (3) Å, respectively, on opposite sides of the mean plane formed by the remaining ring atoms. The crystal structure is stabilized by inter-molecular hydrogen bonds of the types O-H⋯O and C-H⋯O; the former result in dimers lying about inversion centers and the latter form chains of mol-ecules running along the c axis. In addition, intra-molecular O-H⋯O links are present.