Fangatau, or Nakai-erua, is a small atoll in the Tuamotu group in French Polynesia. The nearest land is Fakahina Atoll, located 72 km to the ESE. This small atoll has an elongated shape. Its length is , maximum width . It has a total area of , land area 5.9 km<sup>2</sup>. Its reef encloses its lagoon completely. Anchorage is difficult. Fangatau Atoll has 150 inhabitants (2022 census). Teana is the main village.
The first recorded European to arrive at Fangatau was Russian explorer Fabian Gottlieb von Bellingshausen on the 10 July 1820 on ships Vostok and Mirni. He named this atoll "Arakcheev". Fangatau was the home of Kamake an Iturangi, regarded by anthropologist Kenneth Emory as "the greatest Tuamotuan sage" he ever met.
The commune of Fangatau consists of Fangatau Atoll, as well as the atoll and associated commune of Fakahina. The seat of the commune is the village Teana.
The atoll is served by the Fangatau Airport .