In enzymology, an alkanesulfonate monooxygenase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are alkanesulfonate (R-CH<sub>2</sub>-SO<sub>3</sub>H), FMNH<sub>2</sub>, and O<sub>2</sub>, whereas its 4 products are aldehyde, FMN, sulfite, and H<sub>2</sub>O.
This enzyme belongs to the family of oxidoreductases, specifically those acting on paired donors, with O<sub>2</sub> as oxidant and incorporation or reduction of oxygen. The oxygen incorporated need not be derived from O<sub>2</sub> with reduced flavin or flavoprotein as one donor, and incorporation of one atom of oxygen into the other donor. The systematic name of this enzyme class is alkanesulfonate, reduced-FMN:oxygen oxidoreductase. Other names in common use include SsuD, and sulfate starvation-induced protein 6.