β-Mannosidase (EC 3.2.1.25}, mannanase, mannase, β-D-mannosidase, β-mannoside mannohydrolase, exo-β-D-mannanase, lysosomal β A mannosidase) is an enzyme with systematic name β-D-mannoside mannohydrolase, which is in humans encoded by the MANBA gene. This enzyme catalyses the following chemical reaction

This gene encodes a member of the glycosyl hydrolase 2 family. The encoded protein localizes to the lysosome where it is the final exoglycosidase in the pathway for N-linked glycoprotein oligosaccharide catabolism. Mutations in this gene are associated with β-mannosidosis, a lysosomal storage disease that has a wide spectrum of neurological involvement.