Moloaûa Bay is on the northeast shore on the island of Kauai in Hawaii. The bay is long.
The name comes from molo aa in the Hawaiian language which means "matted roots". Paper Mulberry trees (Broussonetia papyrifera, or wauke in Hawaiian) once grew so thickly that the roots were interwoven. The Moloaûa Stream empties into the north end of a beach which is backed by high cliffs. Uphill from the bay is the Moloaûa State Forest Reserve.
Moloaûa Bay had one of the highest runups in Kauai during the April 1, 1946 tsunami from the 1946 Aleutian Islands earthquake. It experienced one of the highest wave amplitudes: .
Some scenes in the Gilligan's Island pilot were filmed in Moloaûa Bay.