In the title compound, C(13)H(15)NO(5)S, the thia-zine ring adopts a distorted half-chair conformation. The enolic H atom is involved in an intra-molecular O-H⋯O hydrogen bond, forming a six-membered ring. In the crystal, mol-ecules are linked through weak inter-molecular C-H⋯O hydrogen bonds, resulting in zigzag chains lying along the c axis.