Merdø
| Location in southern Norway | |
| Geography | |
|---|---|
| Location | Agder, Norway | 
| Coordinates | 58°25′29″N 8°48′01″E / 58.4246°N 08.8002°E | 
| Area | 0.3 km2 (0.12 sq mi) | 
| Length | 1.3 km (0.81 mi) | 
| Width | 500 m (1600 ft) | 
| Administration | |
| Norway | |
| County | Agder | 
| Municipality | Arendal | 
| Demographics | |
| Population | 0 (permanent) (2017) | 
| Pop. density | 0/km2 (0/sq mi) | 
Merdø is an island in Arendal municipality in Agder county, Norway. The 0.3-square-kilometre (74-acre) island lies along the Skagerrak coast, near the entrance to the Galtesundet, the main shipping channel leading to the town of Arendal on the mainland. The islands of Tromøy and Hisøya lie to the north and northwest. The small islands of Ærøya and Havsøya lie to the southwest. A part of the island is included in Raet National Park.