In 1941 Carole starred in the Technicolor musical Moon Over Miami. Carole is Barbara Latimer, a carhop who helps her sister find a wealthy husband in Miami. This was the first film she made after signing with 20th Century Fox. Betty Grable plays Barbara's sister Kay who pretends to be rich so she can marry a millionaire. They were cast as sisters again in the 1941 drama I Wake Up Screaming. Betty and Carole hated each other and their feud was written about in gossip columns. Carole demanded that the studio give her a dressing room that was as big as Betty's. Moon Over Miami was filmed at Fox studios from March 3 until April 25, 1941. Several of the outdoor scenes were filmed on location in Florida.
The cast included Robert Cummings, Don Ameche, Jack Haley, Charlotte Greenwood, and Cobina Wright Jr. Moon Over Miami was directed by Walter Lang. The original title for the movie was "Miami". Carole sings several songs including "Oh Me, Oh Mi-Ami" and "What Can I Do For You". The costumes were designed by Travis Banton. Moon Over Miami was a remake of the 1938 film Three Blind Mice. Fox made another version in 1946 with the title Three Little Girls In Blue. Moon Over Miami premiered in Miami, Florida on June 18, 1941 and it was released across the country on July 4. It became one of the most popular musicals of 1941. Carole only had a supporting role but she got wonderful reviews for her performance.