The Mexican Senate has repealed part of the Federal Criminal Code that made adultery an offence punishable by two years in prison.
Senators voted with 69 in favour and one abstention to get rid of a law they said was never enforced but remained on the books.
Pablo Gomez of the leftist Democratic Revolution Party said the law was part of a legal construct that historically allowed men to hold women as property.
The change already passed the lower House of Deputies and now goes to President Felipe Calderon for his signature.