In the title compound, C(17)H(15)NO(5)S, the benzene ring of the fused-ring system is twisted by 11.67 (6)° with respect to the thia-zine ring. The atoms of the four-atom methyl ester group and the phenyl ring of the benzyl unit are inclined at 16.50 (7) and 44.52 (3)° with respect to the thia-zine ring. An intra-molecular O-H⋯O hydrogen bond gives rise to a six-membered S(6) ring motif. In the crystal, mol-ecules are extended through a C-H⋯O inter-action along the a axis. C-H⋯π inter-actions are also observed.