Hyposmocoma opuumaloo is a species of moth of the family Cosmopterigidae. It is endemic to Necker Island. The type locality is Flagpole Hill.
The wingspan is 8.9–9.1 mm.
The larval case is cone-shaped and 6.7–7.1 mm in length.
Adults were reared from case-making larvae. Larvae were collected on the ground.