The pontiff was met by hundreds of well-wishers in Cartagena, Colombia, on the last day of his visit to the south American country.
He lost his balance when his motorcade came to an abrupt halt, bruising his left eye and cutting his left eyebrow which dripped blood onto his white cassock.
The cut was swiftly treated with ice and bandaged up.
After the morning's dramas, the 80-year-old prayed at the tomb of St. Peter Claver, the 17th century missionary who ministered to hundreds of thousands of African slaves who were brought to be sold through Cartagena's port during Spanish colonial times.
Francis, known for his own simple and austere style, said Claver was "austere and charitable to the point of heroism."