The vice-consul, who was not identified, "was hit in the foot by a shot from a firearm" while in Angra dos Reis, Rio state police said in a statement.
The victim was taken to Samaritano Hospital in Rio de Janeiro "to undergo an operation."
The US embassy said it would issue a statement later on the incident. The hospital would not comment.
A British tourist was shot and wounded in Angra dos Reis in August when she, her husband and their three children accidentally drove into a favela controlled by criminals.