After his brother Yata is lost at sea, young Ryota steals a yacht with his two friends and a bank robber. This motley crew runs afoul of sea monster Ebirah, and washes up on the shore of Devil's Island, where a terrorist organization manufactures heavy water for their nefarious purposes, as well as a chemical that keeps Ebirah at bay. The organization, Red Bamboo, has enslaved natives from Infant Island to help them, but the natives hope to awaken a dormant Mothra to rescue them. In their efforts to avoid capture, Ryota and his friends, aided by a beautiful native girl, stumble across Godzilla sleeping within a cliffside cavern. The group devises a plan to defeat the Red Bamboo and escape from the island. In the process, they wake Godzilla using a lightning rod. Godzilla fights Ebirah, but the giant shrimp escapes. Godzilla is then attacked by a giant condor and a squadron of Red Bamboo fighter jets, but destroys them. The humans retrieve the missing Yata, free the enslaved natives and Godzilla begins to destroy the base. Godzilla smashes a tower that has a self destruct button that makes the island unstable. Godzilla fights Ebirah and defeats it, ripping off both Ebirah's claws and causing it to retreat into the sea. The natives summon Mothra to save everyone, however, Godzilla challenges Mothra when she gets to the island. Mothra manages to push Godzilla away and carry the people off. Godzilla escapes the island just before it explodes.
- Akira Takarada as Yoshimura
- Tooru Watanabe as Ryota Kane
- Tooru Ibuki as Yata Kane
- Choutarou Tougin as Ichino
- Hideo Sunazuka as Nita
- Kumi Mizuno as Dayo
- Pair Bambi as Shobijin
- Jun Tazaki as Red Bamboo Commander
- Akihiko Hirata as Captain Ryuui (Yamoto in English version)
- Eisei Amamoto as Carrier Captain
- Haruo Nakajima as Godzilla
- Yū Sekida as Ebirah
In 1967, the film was released directly to television in North America by the Walter Reade Organization. It was the first Godzilla film to not receive North American theatrical distribution.
There were several small alterations made: Dialogue was dubbed to English.
Captain Ryuui's name was changed to Yamoto.
Deleted: The opening credits sequence. This version features only the title card, Godzilla vs. the Sea Monster.
Deleted: A scene where Ryoto goes to the Maritime Safety office and sees a poster on the wall for a dance contest.
Deleted: Rock music that played in the Japanese version during Godzilla and Ebirah's battle.
- The film originally didn't involve Godzilla, but was meant for King Kong. That explains why Godzilla was revived by lightning and why the opposing monsters in the film have no special abilities. It may also explain why Godzilla fights Mothra, despite becoming allies previously, because King Kong had never met Mothra.
- The Godzilla suit used for this film is the same "DaisensoGoji" suit used the previous year for Invasion of Astro-Monster, this is the last movie where this suit gets used throughout.
- In the original Japanese trailer a remix of A Night on Bald Mountain is used as the trailers BGM (Background Music).
- This film represents a change in the direction of the series as a whole. This is mostly due to the new faces behind the scenes. Although Tomoyuki Tanaka, Eiji Tsuburaya, and Sinichi Sekizawa returned to produce, direct the special effects, and pen the screenplay (respectively), the film features new director Jun Fukuda, who would direct the next year's Son of Godzilla, and return to direct Godzilla vs. Gigan, Godzilla vs. Megalon, and Godzilla vs. Mechagodzilla' in the 1970's. Musical composer Masaru Sato, who had scored Godzilla Raids Again in 1955 (as well as many of Akira Kurosawa's films) returns to provide the jazzy and contemporary score for this film. Sato, like Fukuda, would return to write music for Son of Godzilla and Godzilla vs. Mechagodzilla.
- The English version runs 83 minutes, four minutes shorter than the Japanese version, and was featured in an episode of the movie-mocking television series Mystery Science Theater 3000.