Ilha Grande (Portuguese pronunciation: [ˈiʎɐ ˈɡɾɐ̃dʒi] "Big Island") is an island located off the coast of Rio de Janeiro state, Brazil. The island, which is part of the municipality of Angra dos Reis, remains largely undeveloped. For almost a century it was closed by the Brazilian government to free movement or settlement because it first housed a leper colony and later a top-security prison (Colônia Penal de Dois Rios, later known as Instituto Penal Cândido Mendes). The Cândido Mendes prison, which housed some of the most dangerous prisoners within the Brazilian penal system, was finally closed in 1994. The largest village on the island is called Vila do Abraão with approximately 1900 inhabitants.

The island, which is 193 km² (75 sq mi) in area, is now a popular tourist destination that is noted for its scenic beauty, unspoiled tropical beaches, luxuriant vegetation and rugged landscape. The highest point is the 1,031 m (3,383 ft) Pico da Pedra D'Água. Most of its territory is within the Ilha Grande State Park. The remainder of the island is subject to stringent development restrictions.

On 5 July 2019, Ilha Grande and Paraty were inscribed as a UNESCO World Heritage Site.