The Unpardonable Sin is a 1919 American silent drama/propaganda film set during World War I. The film was produced by Harry Garson, directed by Marshall Neilan, and stars Neilan's wife Blanche Sweet whose portrays dual roles in the film. The Unpardonable Sin is based on the novel of the same name by Rupert Hughes. Its survival status is classified as unknown, suggesting that it is a lost film.