Pétrus Ky (December 6, 1837 - September 1, 1898) in Vĩnh Long Province, Vietnam, also called Trương Vĩnh Ký and Jean-Baptiste Pétrus, was a Vietnamese scholar whose publications helped improve understanding between colonial Vietnam and Europe. His works helped popularize the romanized script of the Vietnamese language, Quốc Ngữ, leading to its officialization in the early 20th century.
He served in the French colonial regime as a linguist and as such is a controversial figure in Vietnam.