Hyposmocoma mokumana is a species of moth of the family Cosmopterigidae. It is endemic to Necker Island. The type locality is Annexation Hill.
The wingspan is 11.4–14.3 mm.
The larval case is purse-shaped and 7.4–8.9 mm in length.
Adults were reared from case-making larvae. Cases were collected in Sesbania litter.