Casa da Pólvora, Military gunpowder magazine on Ilha da Casa da Pólvora, Porto Alegre, Brazil.

Casa da Pólvora is a former military powder magazine on the Ilha da Casa da Pólvora, a low, flood-prone island in the Guaíba delta facing Porto Alegre's old port. Its surviving buildings are the paiol (magazine), the guardhouse and the Casa da Chácara, restored between 1998 and 2001 to house the Ecomuseu Jacques-Yves Cousteau.

The first powder store was a small warehouse set up in 1773 at the corner of today's Riachuelo and General Vasco Alves streets. A replacement built after 1803 at Ponta do Melo exploded when struck by lightning in 1831. The definitive magazine on Ilha das Pedras Brancas was completed on 17 July 1860 and stayed in use until the 1930s.

The buildings reflect military construction methods from Rio Grande do Sul and sit within a protected natural reserve. Visitors can observe how the structures relate to their island setting and the river landscape around them.

The site is visible from Porto Alegre's waterfront, but the wooden pier to the island needs significant repairs before it is safe to cross. Check access conditions before planning a visit, as the structures may not always be accessible to the public.

The island chosen in 1856 for the powder magazine was the Ilha do Paiva, ceded free of charge by its owner, Israel Soares de Paiva. Its low, flood-prone ground proved unsuitable, so the definitive magazine was built instead on the rocky Ilha das Pedras Brancas, completed on 17 July 1860.