São Miguel das Missões (Portuguese pronunciation: [sɐ̃w̃ miˈgɛw das misˈõȷ̃s]) (Portuguese for St. Michael of the Missions) is a Unesco World Heritage site located in the small town of São Miguel das Missões in the northwestern region of Rio Grande do Sul, a state in southern Brazil. It is also known as São Miguel Arcanjo and by its Spanish language name San Miguel. It was one of the many Spanish Jesuit Reductions in Argentina, Brazil, Paraguay and Bolivia. Jesuit missionaries founded the mission in the 18th century in part to catechise the Guaraní Indian population and to protect the natives from the Portuguese slave traders known as the Bandeirantes.
The mission was built between 1735 to around 1745. The Treaty of Madrid in 1750 handed sovereignty over the area from Spain to Portugal and the Jesuits were ordered to leave. Their refusal to comply led to the mission's termination in a battle with a Portuguese-Spanish army which had been sent to enforce the newly agreed upon frontier between the two colonial powers. The cathedral in nearby Santo Ângelo city is modeled after the São Miguel das Missões reduction.
The ruins of São Miguel das Missões are protected by UNESCO since 1983.