Ilha do Cabo Frio Biological Reserve, Protected coastal reserve in Arraial do Cabo, Brazil.

The reserve is located on an island near Arraial do Cabo and includes forest terrain, coastal dunes, and lagoons with high salt content. The island covers approximately 700 hectares and features steep cliffs and flat areas that create different habitats.

The reserve was created by Artigo 184 of the Lei Orgânica Municipal of 1990 and is run by the municipality of Arraial do Cabo. Its stated aim is full conservation of the biota and natural features without direct human interference, so public and scientific visits are restricted. UNESCO lists the island within the Atlantic Forest Biosphere Reserve.

The reserve takes its name from the nearby headland and serves as a place where visitors can observe rare plant and animal species found on the island. It demonstrates how isolated islands develop and maintain their own distinct ecological communities.

Access to the island is limited and requires advance permission from the management authorities. Visits are approved primarily for scientific research and educational purposes.

The island is influenced by a cold ocean current that brings nutrient-rich water to the surface and supports specialized plant communities. These conditions create an environment found in few other places along the Brazilian coast.