As a children's film, Toho pressured their filmmakers to show more gore in the monster fights. Children's media in Japan at the time was showing increasing amounts of violence, especially when compared to the rest of the world. Films from rival studios would should monsters frequently bleeding, while popular Japanese superhero TV shows had the superheroes routinely slice, decapitate, and overall mutilate their monster opponents. However, special effects director Eiji Tsuburaya felt that such violence was inappropriate to show on the big screen and when Toho wanted Gorosaurus to bleed profusely after King Kong tore his jaws apart, Tsuburaya snapped back, saying "These movies are for kids. Why do you enjoy showing them blood?" The compromise was for Gorosaurus to foam at the mouth instead.
The voice of Dr. Who and several other male characters in this film was the legendary Paul Frees, the Man of a Thousand Voices, who also voiced both Burgermeister Meisterburger and Grimsby in the Rankin/Bass Christmas TV special Santa Claus is Comin' to Town (1970).
Even though Linda Miller was an American who spoke fluent English, her voice in the film was dubbed by Julie Bennett.
King Kong's human friends Dr. Bond, his son Bobby, his daughter Susan and Captain Englehorn from the animated TV series The King Kong Show (1966) were eliminated from the film and replaced by the characters that are in the film.
The original Japanese version of this film has never been officially released in the West in any form of media.