The film took 10 months to make in total, though in between gaps in filming Capra's crew managed to squeeze in Richard Boleslawski's Theodora Goes Wild.
The Lamasery set was, at the time, the largest single standing set in terms of square feet built for a motion picture of the sound era. The set was built on the Columbia ranch in Burbank with the rear of the Lamasery backing up to the intersection of Verdugo Avenue and Hollywood Way.
The part of the paleontologist was not in the original novel but was developed for Horton by Capra. Horton improvised the scene when he is startled by the mirror in the lacquer box when Capra asked him to suggest some business for that scene.
The parts played by Margo and Jane Wyatt were one character in James Hilton's original novel.