In enzymology, a 3-deoxyoctulosonase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are 3-deoxyoctulosonyl-lipopolysaccharide and H<sub>2</sub>O, whereas its two products are 3-deoxyoctulosonic acid and lipopolysaccharide.
This enzyme belongs to the family of hydrolases, specifically those glycosidases that hydrolyse O- and S-glycosyl compounds. The systematic name of this enzyme class is 3-deoxyoctulosonyl-lipopolysaccharide hydrolase. This enzyme is also called alpha-Kdo-ase.