The Secret of NIMH is a 1982 American animated fantasy adventure film directed by Don Bluth in his directorial debut and based on Robert C. O'Brien's children's novel, Mrs. Frisby and the Rats of NIMH. It features an ensemble cast consisting of Elizabeth Hartman in her final film role as its protagonist, Mrs. Brisby, with Peter Strauss, Arthur Malet, Dom DeLuise, John Carradine, Derek Jacobi, Hermione Baddeley and Paul Shenar in supporting roles. It was produced by Bluth's production company Don Bluth Productions in association with Aurora Productions.

The Secret of NIMH was released in the United States on July 2, 1982, by MGM/UA Entertainment Co. under the United Artists label. It was praised by critics for its elegant and painstakingly detailed animation, compelling characters, and deep and mature plot, and won a Saturn Award for Best Animated Film of 1982. Though only a moderate success at the box office, it turned a solid profit through home video and overseas releases. It was followed in 1998 by a direct-to-video sequel, The Secret of NIMH 2: Timmy to the Rescue, which was made without Bluth's involvement or input and met with poor reception.

In 2015, a live-action/animated remake was reported to be in the works. A television series adaptation was also revealed to be in development since 2021.