The title compound, C16H12NOSSe+·HSO4 −, was obtained from a mixture of 3-(4-methoxyphenyl)[1,3]selenazolo[2,3-b][1,3]benzothiazol-4-ium chloride and potassium hydrogen sulfate. In the cation, the benzene ring is twisted by 71.62 (7)° from the tricycle mean plane. In the crystal, O—H⋯O hydrogen bonds link the anions into chains along [100]. The anions in adjacent chains are linked via weak C—H⋯O hydrogen bonds. The crystal packing exhibits short intermolecular contacts between the chalcogen unit and the O atoms: Se⋯O(anion) 2.713 (3), Se⋯O(cation) 2.987 (3) and S⋯O(anion) 2.958 (3) Å.