Shortly before his death in 1993, director Ishirô Honda was said to have mentioned that this was his favorite of all his films.
Yoshio Tsuchiya was offered the lead role but turned it down, instead opting to play the Mysterian leader. Tsuchiya, known for his work in the films of Akira Kurosawa, enjoyed working on Toho's science fiction films. and preferred to play alien characters.
This was one of the last films to be distributed by RKO in the US. When RKO ceased operations, most of the first run was handled by MGM.
Mogera, the giant robot that was added to the film, was created to be a Godzilla-like mechanical monster, including spines along the back and a large tail. In the final edit of the film, most of the selected shots hide the fact that the robot does have a tail.
Martin Scorsese has expressed admiration for the imagination of this film and other Toho science fiction films when he wrote the forward to the director's biography.