Júlio de Castilhos Museum, Historical museum in Centro Histórico, Porto Alegre, Brazil.

The Júlio de Castilhos Museum is a history museum housed in a listed building in Porto Alegre's historic center, dedicated to the story of Rio Grande do Sul. The collection brings together paintings, everyday objects, photographs, and documents from different periods of the state's past.

The museum was founded in 1903, the culmination of earlier attempts to create a state museum in Rio Grande do Sul, and is the oldest museum in the state still in operation. In 1897 governor Júlio de Castilhos proposed a state museum, and Law No. 29 of 1899 authorised up to 50 contos de réis for its creation. It is named after him.

The museum's collection exceeds ten thousand pieces, mostly tied to the history of Rio Grande do Sul, and its sections on the Ragamuffin War and the Paraguayan War are especially rich. It also keeps a few sculptures made by Jesuits and indigenous peoples in the Indian Reductions. In September 2023 a flood damaged part of the collection, and 150 works were restored the following year.

The museum sits in the city center of Porto Alegre and is easy to reach by public transport. A visit pairs well with a walk through the surrounding historic center, which has other buildings and squares worth seeing nearby.

The museum keeps a reconstructed bedroom of Júlio de Castilhos, furnished with original pieces and personal belongings from his last years. This room is one of the few places in the city where you can get close to the private life of a key figure from the region's past.