Mary Astor's Purple Diary is a book by cartoonist Edward Sorel. It tells the story of a 1936 Hollywood sex scandal involving Mary Astor, star of The Maltese Falcon (1941). The scandal revolved around Astor's private diary, which her estranged husband, Dr. Franklyn Thorpe, stole and used in a bitter custody battle.

The diary's incriminating contents forced Astor to give up custody of their daughter in order to obtain a divorce. When Astor decided to fight back for custody of their 4-year-old daughter, the book set off a scandal that knocked news of Hitler off the front page.
The book is partially an account of the trial, partially a biography of Astor, and partially a memoir of Sorel himself.