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, written by Kathryn Stuart, and stars Neilan's wife, Blanche Sweet, who portrays dual roles in the film. The Unpardonable Sin is based on the novel of the same name by Rupert Hughes. The Silent Era site reports that it is not known whether the film currently survives, suggesting that it is a lost film. However, prints and/or fragments did turn up in the Dawson Film Find in 1978, so some of it at least survives.