The Belles of St Trinian's is a 1954 British comedy film, directed by Frank Launder, co-written by Launder and Sidney Gilliat, and starring Alastair Sim, Joyce Grenfell, George Cole, Hermione Baddeley. Inspired by British cartoonist Ronald Searle's St Trinian's School comic strips, the film focuses on the lives of the students and teachers of the fictional school, dealing with attempts to shut them down while their headmistress faces issues with financial troubles, which culminates in the students thwarting a scheme involving a racehorse.

The film was among some of the most popular British films to be released in 1954, with critics praising the comedy and several of the cast members for their performances, including Sim's dual role as the headmistress Miss Millicent Fritton and her twin brother Clarence Fritton. The film was the first to be produced in the St. Trinian's film series – three sequels were later produced and released after this film: Blue Murder at St Trinian's (1957); The Pure Hell of St Trinian's (1960); and The Great St Trinian's Train Robbery (1966).