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 students and teachers of the fictional school, dealing with attempts to shut it down while the headmistress faces financial troubles, which culminates in students thwarting a scheme involving a racehorse.

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