In the title mol-ecule, C(16)H(14)N(2)O(4)S, the thia-zine ring adopts a twist chair conformation with the N and adjacent C atom displaced by 0.966 (3) and 0.386 (4) Å, respectively, on the same side of the mean plane formed by the remaining ring atoms. The dihedral angle between the mean planes of the benzene rings is 37.65 (10)°. The mol-ecular structure features an intra-molecular O-H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, mol-ecules are linked by N-H⋯O and C-H⋯O hydrogen bonds.