Kiwai Island is the largest island in the Fly River delta, Papua New Guinea. It is 59 km long along the northwest-southeast axis from Wamimuba Point in the northwest to the village of Saguane (Sanguane) in the south, and up to 9 km wide, with an average width of 5.6 km. Its area is 359 km² . Neighboring Purutu and Wabuda Islands to the north and northeast are also among the three largest islands in the Fly River delta. The island has a population of about 4500.
The island separates the north and south entrances of the Fly River. It is well wooded and only a few feet above water. The chief village, Iasa, is located on the south side of the island. Sumai village is on the same side of the island and 24 km farther northwest. Doropo village is about midway along the north side of the island. At the east end of the island are other small villages, such as Sagasia, Ipisia, Agobara and Oromosapuo.