Diary of a Lost Woman (German: Das Tagebuch einer Verlorenen) is a 1918 German silent drama film directed by Richard Oswald and starring Erna Morena, Reinhold Schünzel, and Werner Krauss. The rising star Conrad Veidt also appeared. It is now considered a lost film. It was remade at the end of the silent era as Diary of a Lost Girl by Georg Wilhelm Pabst.

Due to the film's over theme of prostitution it had major censorship issues which delayed its release for several months and led to a number of cuts.The film's sets were designed by the art director August Rinaldi.