Mothra vs. Godzilla (Japanese: モスラ対ゴジラ, Hepburn: Mosura tai Gojira) is a 1964 Japanese kaiju film directed by Ishirō Honda, with special effects by Eiji Tsuburaya. Produced and distributed by Toho Co., Ltd., it is the fourth film in the Godzilla franchise. The film stars Akira Takarada, Yuriko Hoshi, Hiroshi Koizumi, Kenji Sahara, and Emi and Yumi Itō, with Haruo Nakajima and Katsumi Tezuka as Godzilla. In the film, humans beseech the aid of the insect god Mothra to stop Godzilla from destroying Japan.

Due to the success of Mothra (1961) and King Kong vs. Godzilla (1962), Toho chose to pair Godzilla against Mothra for the following film. The film was intended for children as well as adults, as a way to compete with television's growing popularity in Japan. A new Godzilla suit and Mothra prop were built although the 1962 Godzilla suit was used for water scenes. At Tsuburaya's insistence, Toho purchased an Oxberry 1900 optical printer to remove damages in composite photography shots. It is the final film in the franchise's Shōwa era to depict Godzilla as the antagonist.

Mothra vs. Godzilla was released theatrically in Japan on April 29, 1964. An edited version titled Godzilla vs. the Thing was released by American International Pictures in the United States on August 26, 1964. The film received generally positive reviews from early and contemporary American critics. American film historians have praised the film's themes of unity, greed, and Honda's depiction of Godzilla as a "specter of nuclear annihilation" and a symbol of moral judgement.

The film was followed by the fifth film in the Godzilla franchise Ghidorah, the Three-Headed Monster, released on December 20, 1964.