Una Biological Reserve, Biological reserve in Ilhéus, Brazil.

Una Biological Reserve covers 18,715 hectares of Atlantic Forest in southern Bahia, 45 km south of Ilhéus. Its terrain runs from flat coastal plain to plateaus of 200–300 m, cut by the Serra and Maruim rivers. Two forest types occur: sandy-soil tabuleiro forest in the east and submontane humid forest, with at least 1,038 vascular plant species.

Una Biological Reserve was created on 10 December 1980 to protect the golden-headed lion tamarin, a primate endemic to the Atlantic Forest of southern Bahia. In 2002 it became part of the Central Atlantic Forest Ecological Corridor, a network linking protected areas across the region.

The reserve is named after the Una River, fed by the Aliança and São Pedro rivers. In its surroundings, cacao is grown in the cabruca system, an agroforestry method where cacao shrubs are shaded by trees left from the original forest. The reserve was the main protected area created for the golden-headed lion tamarin, endemic to the Atlantic Forest of southern Bahia.

The reserve lies about 45 km south of Ilhéus, in the Una municipality, and is reached via the BA-001 coastal road. As a strict nature reserve (IUCN category Ia), entry is only allowed with a licence issued by the reserve manager, so request authorisation from the managing office before travelling. The Serra River crosses the reserve from west to south-east, and the Maruim forms its north-west border.

The reserve was created mainly to protect the golden-headed lion tamarin (Leontopithecus chrysomelas), a primate endemic to the Atlantic Forest of southern Bahia. The Serra River crosses the reserve from west to south-east, and the Maruim River forms its north-western natural border.