The Rossio Massacre took place on the evening of 13 March 1838, when forces loyal to the Portuguese government of Prime Minister Sá da Bandeira put down a revolt by radical sections of the National Guard and their supporters, who were gathered in Rossio Square in central Lisbon. Around 100 people were killed, and an unknown number injured. Contemporary accounts agree on the events leading up to the massacre, but differ in their description of how it took place and who the victims were.

The Rossio is the popular name of the King Pedro IV Square in the city of Lisbon, in Portugal. It is located in the Pombaline Downtown of Lisbon and has been one of its main squares since the Middle Ages. It has been the setting of popular revolts and celebrations, bullfights and executions, and is now a preferred meeting place of Lisbon natives and tourists alike.