Anthraquinone-1-sulfonic acid is an organic compound with the formula . It is one of two of monosulfonated anthraquinone isomers. The compound is prepared by mercury-catalyzed reaction of anthraquinone with oleum. It undergoes chlorination (the Fischer reaction) to give 1-chloroanthraquinone. Its potassium salt is called "Diament salt".
It is a precursor to several dyes.
The pervasive use of sulfonated dyes has led to the development of analytical methods.