In the title compound, C(18)H(17)NO(5)S, the thia-zine ring adopts a half-chair conformation and the dihedral angle between the aromatic rings is 79.41 (6)°. An intra-molecular O-H⋯O hydrogen bond generates an S(6) ring. In the crystal, mol-ecules are linked by weak C-H⋯O inter-actions resulting in infinite sheets along the b and c axes.