The molecule of the zwitterionic title compound, C(6)H(9)NO(4)S, which lies on a mirror plane, shows a puckered chair conformation of the six-membered ring with the S and N atoms out of the mean plane of the other four C atoms by 0.929 (2) and 0.647 (2) Å, respectively. The ionized carboxyl group is equatorially oriented. The hydrogen-bonding network includes very short O-H⋯O [2.470 (2) Å] and N-H⋯S [3.471 (2) and 3.416 (2) Å] inter-molecular contacts.