Julie Andrews initially turned down the role of Miss Eglantine Price. She eventually reconsidered, believing she owed her movie career to Walt Disney Studios and wanted to work there again. When she told the studio she'd changed her mind, Dame Angela Lansbury had already been cast.
Angela Lansbury hated what she called "by the numbers" acting in this movie. Due to the heavy special effects, the entire movie had to be storyboarded in advance, shot for shot. Every moment was pre-determined, and Lansbury wasn't free to explore her character naturally.
This movie was developed at the same time as Mary Poppins (1964). Walt Disney started with this movie, decided it was too complicated technically, and switched over to Mary Poppins. They switched back and forth between movies a few times. They intended to drop this movie permanently at one point, but The Sherman Brothers, who did the music for both projects, insisted that Disney finish it after they were done with Mary Poppins.
(at around 39 mins) Several of the dolls Carrie admires in the nursery of Professor Emelius Browne's house were modelled after the international puppets in the Small World ride at Disneyland.
This was the last Disney movie released while Roy O. Disney was still alive. He died a week after its U.S. premiere.