The title compound, C(9)H(9)NO(6)S, was prepared by the reaction of methanol and thionyl chloride with 4-methyl-sulfonyl-2-nitro-benzoic acid under mild conditions. The dihedral angle between the nitro group and benzene ring is 21.33 (19)° and that between the carboxyl-ate group and the benzene ring is 72.09 (17)°. The crystal structure is stabilized by weak inter-molecular bifurcated C-H⋯O inter-actions occurring in the (100) plane.