| Map: | Guinea-Bissau |
| Archipelago: | Bissagos Islands |
| Country: | Guinea-Bissau |
| Area Km2: | 140 |
| Country Admin Divisions Title: | Region |
| Country Admin Divisions: | Bolama |
| Coordinates: | 11.4833°N -73°W |
| Population As Of: | 2009 |
| Population: | 1,873 |
Formosa is an island in the Bissagos Islands, Guinea-Bissau, part of the sector of Caravela. Its area is 140 km2,[1] its length is 19.9 km and its width is 10 km. It forms practically one island with Ponta and Maio, separated by creeks. The island has a population of 1,873 (2009 census); the largest village is Abú.[2]