If you are interested in information about how to renounce or relinquish your U.S. citizenship in Brazil, please visit https://br.usembassy.gov/expatriation-or-renunciation-of-u-s-citizenship/ . Loss of U.S. citizenship is a serious and irrevocable act which deserves your thoughtful consideration. Please do not schedule a Loss of Nationality appointment using our online calendar. All appointments for this service will be scheduled by email only.

Brasília – brasiliaacs@state.gov
Porto Alegre – portoalegreacs@state.gov
Recife – recifeacs@state.gov
Rio de Janeiro – acsrio@state.gov
São Paulo – saopauloacs@state.gov

General information is available at https://travel.state.gov/content/travel/en/legal/travel-legal-considerations/us-citizenship/Relinquishing-US-Nationality-Abroad.html .