Let's Kill Uncle—also known as Let's Kill Uncle Before Uncle Kills Us—is a 1966 color black comedy film produced and directed by William Castle, about a young boy trapped on an island by his uncle, who is planning to kill him. The boy's only friend is a young girl, who tries to help him.

It stars Nigel Green, Mary Badham, Pat Cardi and Robert Pickering and is based on a 1963 novel written by Rohan O'Grady, the pen name of Canadian author June Margaret O'Grady Skinner. It was filmed in Universal Studios on the largest sound stage, taking advantage of the process screen, with a location shot of a beach in Malibu, California.