The hexopyranosyl ring of the title compound, [Hg(CH(3))(C(9)H(15)O(7)S)], adopts the (4)C(1) chair conformation, and the anomeric configuration of the thiomethylmercury linkage is beta. The compound exists as two symmetry-independent conformers, A and B, within the unit cell, and each shows an almost linear S-Hg-C arrangement. Most of the bond distances and angles in A and B are similar, although a marked difference exists in the side-chain conformation. Weak secondary intramolecular (between Hg and ring O) and intermolecular (between A and B conformers) interactions are documented.