Brazil shares a border with France through French Guiana, France's overseas department on the northeastern coast of South America. The border separates French Guiana from Brazil's state of Amapá.
The Brazil–France border runs for roughly 730 kilometers, making it France's longest land border. Much of it follows the Oyapock River, which reaches the Atlantic Ocean near the towns of Saint-Georges-de-l'Oyapock in French Guiana and Oiapoque in Brazil. The Oyapock River Bridge, opened to traffic in 2017, provides a road connection between the two sides.
This answer can seem surprising because France is usually associated with Europe. French Guiana is legally part of France and the European Union, so France has international borders in South America as well as in Europe. The current boundary was settled in Brazil's favor by international arbitration in 1900 after a long territorial dispute between France and Brazil.