This film was originally written to star King Kong. That explains the uncharacteristic behavior of Godzilla, such as: Godzilla is found sleeping in a cave, when previous films have established that Godzilla rests underwater, he is awakened by lightning, just as King Kong was in Kingu Kongu tai Gojira (1962), and most uncharacteristically he is protective of Dayo, more typical of Kong's affection toward women.

This was the final appearance for Mothra's twin priestesses in a "Showa" era film. They later would return in the Heisei era film Gojira vs. Mosura (1992). This was also the first and only time the twin fairies (known as the Shobijin, or Little Beauties) were played by Pair Bambi. The fairies had previously been played by Emi Itô and Yumi Itô, known as The Peanuts.

Ebirah's name came from the Japanese word ebi, which means "shrimp," so technically, Ebirah is a shrimp.

Noriko Takahashi originally started the role of Dayo, but when filming began she suffered from acute appendicitis and was hospitalized. Kumi Mizuno was cast at the last minute. (Although the character of Dayo was intended to be 19, Noriko's age at the time, Kumi was 29.)

After destroying the Giant Condor (Dai-Kondoru), Godzilla rubs his nose. This is an homage to Yûzô Kayama's popular "Yuichi Tanuma" character (from Toho's popular Wakadaishô/Young Guy movies, starting with Daigaku no wakadaishô (1961)), who did the same thing.

This was the final appearance of the "adult" Mothra in a Showa era film. Her next appearance in her adult form would be in the Heisei era film Gojira vs. Mosura (1992).

This was the first of five films in the series to be directed by Jun Fukuda.

This was Akira Takarada's final appearance in a Showa era Godzilla (Gojira) film. His next series appearance would be in the Heisei era film Gojira vs. Mosura (1992).

Contrary to popular belief, the adult Mothra that appeared in this film is not the adult Mothra from Mosura tai Gojira (1964). It was the one metamorphosed from one of the larvae Mothras that appeared in Mosura tai Gojira (1964) and San daikaijû: Chikyû saidai no kessen (1964).

This was the first film in the series to feature an underwater sequence since the original Gojira (1954).

This was the first Godzilla film with special effects directed by Sadamasa Arikawa. Eiji Tsuburaya had just started his own company and only supervised the effects work on this and the next two Godzilla films. Arikawa is uncredited in this film, however, with Tsuburaya receiving an honorary special effects credit.

The Godzilla suit used for this film, the "Daisenso-Goji," was first used in the previous film Kaijû daisensô (1965). During filming, the head of the suit had to be detached and put on the body of the "Mosu-Goji" Godzilla suit (from Mosura tai Gojira (1964)), creating the frilled dinosaur Jirass in Episode #10 ("The Mysterious Dinosaur Base") of "Urutoraman: Kûsô tokusatsu shirîzu" (1966)_. A new head had to be made for the headless Daisenso-Goji suit in short order, with a creepy bug-eyed stare and strange elevated eyebrows. The new look starts at the beginning of Godzilla's siege on the Red Bamboo base. Japanese fans name this revised suit the "Nankai-Goji."

The original title for this film (with Kong as the star) was going to be "Operation Robinson Crusoe".

In Japanese, the Giant Condor's name is "Dai-Kondoru" (or alternatively, "Ôkondoru").

Japan Import DVD has Super-8mm version (Japanese Audio), as a special feature.

If you look closely at the giant condor it is actually a Rodan costume that was redressed for the film.