News reporter Ichiro Sakai and photographer Junko Nakanishi take pictures of a wreckage caused by a typhoon. They uncover a strange, bluish-gray object in the debris, not knowing its significance. Later that day, a giant egg is discovered on the shore. The local villagers salvage it, and an entrepreneur of Happy Enterprises named Kumayama buys the egg from the local villagers. Instead of letting scientists study the egg, Kumayama wants to make it into a large tourist attraction. Later, Sakai and Nakanishi are informed that the strange object they found is extremely radioactive. (It is later hinted that this is a skin particle from Godzilla.)
While Sakai, Nakanishi, and scientist Professor Miura are discussing the egg at a hotel, they discover Kumayama checking in. Kumayama meets with Jiro Torahata, the head of Happy Enterprises. They are unexpectedly confronted by tiny twin girls known as the Shobijin and try to capture them. The Shobijin escape and meet with Sakai, Nakanishi and Professor Miura. They explain that the egg belongs to Mothra. If the egg hatches, the larva (though they have no quarrel with humans) will still cause great damage looking for food. The trio agree to help.
Sakai, Nakanishi and Miura try to reason with Kumayama and Torahata but fail to do so and the Shobijin leave. The three of them return to Kurada Beach, to determine if there is any more radioactive contamination; and, knowing it cannot be Mothra, try to find what the source might be. They soon find it: Godzilla, who had been washed up onto Kurada Beach and buried under mud by the hurricane, suddenly emerges and begins to attack Nagoya. Sakai, Junko, and Miura travel to Infant Island to request the Shobijin to send Mothra to defeat Godzilla. The natives of the island and the Shobijin are eventually convinced by the trio. However, the Shobijin warn them that Mothra is already near death by natural causes.
Kumayama barges into Torahata's room and demands to get his money back that Torahata had recently swindled from him. Kumayama is shot by Torahata, then he too is killed when Godzilla arrives and destroys his hotel. Mothra arrives just when Godzilla reaches her egg and engages Godzilla in battle. Briefly, she seems to be winning, even spraying Godzilla with a poisonous powder, though this is ineffective. Despite giving her all, Godzilla hits her with his atomic breath, and Mothra collapses and dies from exhaustion. Fortunately, Godzilla loses interest in the egg and proceeds with his rampage.
The JSDF launches multiple campaigns against Godzilla until two giant larvae hatch from Mothra's egg. They follow Godzilla to Iwa Island, trap it with their silk spray and force Godzilla into the sea. Sakai, Junko, and Miura thank the Mothra larvae and Shobijin as they return to Infant Island.Akira Takarada as Ichiro Sakai (酒井 市朗, Sakai Ichiro), a reporter
Yuriko Hoshi as Junko Nakanishi (中西 純子, Nakanishi Junko), a photographer
Hiroshi Koizumi as Professor Shunsuke Miura (三浦 俊助 博士, Miura Shunsuke), a scientist
Yū Fujiki as Jiro Nakamura (中村 二郎, Nakamura Jiro), another reporter
The Peanuts, Emi and Yumi Ito, as the Shobijin (小美人, Shobijin), the fairy guardians of Infant Island
Kenji Sahara as Jiro Torahata (虎畑 二郎, Torahata Jiro), a corrupt business tycoon
Jun Tazaki as Maruta (丸田, Maruta), Chief Editor
Yoshifumi Tajima as Kumayama (熊山, Kumayama), owner of Happy Enterprises
With a screenplay written by Shinichi Sekizawa, Mothra vs. Godzilla is a direct sequel to both Mothra and King Kong vs. Godzilla. The film cost about 200 million yen to make, approximately twice the amount the original Godzilla cost.
A new Godzilla costume was created for the film was made by sculptor Teizo Toshimitsu with input from suit actor Haruo Nakajima This led to a lighter costume which allowed for more fluid movement.
Mothra vs. Godzilla was released in Japan on April 29, 1964 where it was distributed by Toho. The Japanese version of the film was released with English subtitles by Classic Media in 2007.
The film was first released in the United States under the title Godzilla vs. the Thing on September 17, 1964 where it was distributed by American International Pictures. The American version of the film contains footage shot by Toho specifically for the American release. The American version of the film received only a few minor adjustments: shortening the twin fairies' song on Infant Island and a scene where Sakai, Junko Miura and Makamura wave goodbye to the Mothras swimming home. Removed scenes include Kumayarma hanging out leaflets to attract visitors to the giant egg incubator and where Torahata shoots Kumayama in a hotel room. New scenes were also added including a sequence where U.S. military officials help Japan against Godzilla. The American release of the film was double-billed with Voyage to the End of the Universe. It was released in 2002 by Sony Wonder Video. This release was dubbed in English.
In a contemporary review from the Monthly Film Bulletin, the review noted that "In spite of some clumsy model shots, Godzilla's fight with the giant moth and its caterpillar progeny is one of Toho's better efforts" The review praised the monsters design in the film and opined that the "ineffectual attempts to bring him to a halt are cleverly and spectacularly staged. Unfortunately, nothing else quite matches the special effects", noting a plot that was "ridiculous" and acting that was "lamentable, and the two miniature twins' habit of repeating every line of dialogue simultaneously is intensely irksome." Variety commented that the film was a "Japanese sci-fi long on special effects but lacks appeal for general trade", and that "inspite of the slick production, the story and acting don't offer enough to attract large genrel audiences." The review commented that "virtually all-Japanese cast, with unfamiliar faces and broad emoting typical of such Japanese pics, also detracts from general appeal." The review commented on the film crew, stating that Honda's direction and the script "keep story moving at lively pace, building up to tense climatic scenes" and that "Eiji Tsuburaya, labored mightily to cook up monsters and their battles, the tiny twins and the military assaults against Godzilla."
From a retrospective review, Steve Ryfle, author of Japan's Favorite Mon-star: The Unauthorized Biography of "The Big G" praised the film as it stood "indisputably as the greatest of all the Godzilla sequels, with a fast-paced story and likable characters, the most impressive Godzilla design ever, two of the Big G's most spectacular battles, and an abundance of special-effects "money shots" that evoke the thrills of the 1954 original."