This is the final film to feature the Itô Sisters (aka the Peanuts) as Mothra's twin priestesses.
The film is noted for beginning the gradual transition of Godzilla's character away from his villainous roots, an idea from producer Tomoyuki Tanaka. While screenwriter Shin'ichi Sekizawa and special effects director Eiji Tsuburaya aided this change by humanizing the monsters and adding more comedy to their antics, director Ishirô Honda opposed it. He was hesitant with the famous monster talk scene but was unable to dispute the studio mandates from Toho. Nevertheless, Honda was troubled by the direction Toho was forcing the series to take, mentioning, "I am concerned that we are drifting toward taking the easy route, believing a silly story line is OK, though it might be mocked by adults simply because the film is made for children. Kids will not tolerate nonsense." Tanaka would come to regret his decision, which he described as a mistake.
Director Ishirô Honda and special effects director Eiji Tsuburaya were known to get together and critique their own work, getting harsher and harsher every time they did. For this film, both men were somewhat disappointed in the execution of the King Ghidorah suit and how it looked in the final film. Honda recalled, "It wasn't easy at all to move. It was so bulky, and not smooth in the air . . . but the kids liked it a lot. It's probably one of our best monsters, and it has an oriental feeling too."
While this was Takashi Shimura's final appearance in a Godzilla film, it was not his final role in a kaiju film as he would appear in Frankenstein vs. Baragon (1965) the following year. Shimura was one of Honda's preferred actors which would often create scheduling conflicts with Akira Kurosawa. Shimura was able to find some time in-between shooting scenes for Red Beard (1965) and was able to film his scenes for this film.
First movie to depict Godzilla less antagonistically and in a somewhat heroic manner. He would gradually develop away from his villainous roots, culminating in his first fully hero role in Godzilla vs. Hedorah (1971). However, series creator Tomoyuki Tanaka would go on to say that making Godzilla heroic was a mistake and how he personally preferred Godzilla to "have a mean streak."