alpha-Mannosidase (, alpha-D-mannosidase, p-nitrophenyl-alpha-mannosidase, alpha-D-mannopyranosidase, 1,2-alpha-mannosidase, 1,2-alpha-D-mannosidase, exo-alpha-mannosidase) is an enzyme involved in the cleavage of the alpha form of mannose. Its system name is alpha-D-mannoside mannohydrolase.