Assumption Island is a small island located at 9°45′S 46°29′E in the Indian Ocean north of Madagascar and is part of the country of the Seychelles. It is a single coral island which measures 11.07 km² in area and which has a small settlement on the sheltered western side. Two large sand dunes are prominent on the southeastern coast of the island, one of them 32 m high. There is a concrete runway that runs from between the two sand dunes on the southeast to the settlement.
It is located about 30 km southest of the Aldabra Atoll and is politically part of the Aldabra Group.
A notable feature of this island is the Assumption Island day gecko. A subspecies of geckos found only on this island.