Naphthalene-2-sulfonic acid is an organic compound with the formula C10H7SO3H.

A colorless, water-soluble solid, it is often available as the mono- and trihydrates C10H7SO3H.2H2O.

The compound is mainly used in the production of dyes via nitration en route to aminonaphthalenesulfonic acids.

[1] Naphthalene-2-sulfonic acid undergoes many reactions, some of which are or were of commercial interest.

Fusion with sodium hydroxide followed by acidification gives 2-naphthol.