This is a list of fictional diaries categorized by type, including fictional works in diary form, diaries appearing in fictional works, and hoax diaries.

The first category, fictional works in diary form, lists fictional works where the story, or a major part of the story, is told in the form of a character's diary. Diary form is frequently used in fiction for young adults and tweens as well as adults. It has been used for multiple books in a series following the diarist's life over many years, such as the Adrian Mole series, the Diary of a Wimpy Kid series, and the Dork Diaries series, all of which chronicle the lives of characters who start a diary as children or adolescents and continue their diary as they mature over time. Fictionalised diaries set during distinct historical periods or events have been used since at least the 1970s to bring history to life for young people. Dear America, My Australian Story and related series are recent examples of this genre. The form is also frequently used for fiction about adult women's lives, some notable examples being Bridget Jones's Diary, The Color Purple, and Pamela.

The second category lists fictional works that are not written in diary form, but in which a character keeps a diary, or a diary is otherwise featured as part of the story. Some common uses for diaries in fiction are to reveal to the reader material that is concealed from other characters, to divulge information about past events, or as a device to provide real or false evidence to investigators in mystery or crime fiction. Examples of diaries being used in one of these ways include Amy Dunne's false diary in Gone Girl and Laura Palmer's secret diary in Twin Peaks.

The third category lists hoax diaries, that were presented as being true diaries of real people when first published, but were later discovered to be fiction. Go Ask Alice, the first of a number of books by Beatrice Sparks purported to be based on diaries of real teenagers, was originally presented by Sparks as the non-fictional diary of an anonymous teenage girl, but was later classified by publishers as fiction.