The giant turtle is known in Japan as Kameba and internationally as Kamoebas. The name is a mixture of kame, the Japanese word for turtle, and amoebas.
This was the last Toho production to be made under the old studio system with the actors being under contract to the studio.
The story was originally going to take place in Guam. However, this was changed to Hachigo Island because the budget wasn't substantial enough to afford shooting on location in Guam.
This was the first giant monster film produced after the death of Toho's special effects director, Eiji Tsuburaya, who passed away in January 1970. Sadamasa Arikawa was promoted to to Director of Special Techniques (special effects) and Teriyoshi Nakano was promoted to his chief assistant.
This film was originally going to be filmed on the Izu peninsula, but this was changed to Hachigo Island because the movie was shot in the wintertime.
All three monsters, the squid Gezora, the crab Ganimes and the turtle Kamoebas have remained relatively obscure and never had a major role in later monster movies made by Toho. However, Gezora gained some notoriety for its appearance as the first boss in Nintendo's Godzilla: Monster of Monsters video game and its brief cameo in Gojira: Fainaru uôzu (2004), and Kamoebas also had a cameo as a carcass washed ashore in Gojira tai Mosura tai Mekagojira: Tôkyô S.O.S. (2003).
Actor Yoshio Tsuchiya convinced his friend Kenji Sahara to switch roles.
The name Gezora was initially rejected for the squid monster because it was too obvious.
The writers originally intended the film's plot to span the globe, but these plans had to be drastically scaled back due to budgetary reasons.