Godzilla vs. Megalon (ゴジラ対メガロ, Gojira tai Megaro) is a 1973 Japanese kaiju film directed by Jun Fukuda, written by Fukuda and Shinichi Sekizawa, and produced by Tomoyuki Tanaka, with special effects by Teruyoshi Nakano. Distributed by Toho and produced under their effects subsidiary Toho–Eizo, it is the 13th film in the Godzilla franchise, and features the fictional monster characters Godzilla, Megalon, and Gigan, along with the mecha character Jet Jaguar. The film stars Katsuhiko Sasaki, Hiroyuki Kawase, Yutaka Hayashi, and Robert Dunham, alongside Shinji Takagi as Godzilla, Hideto Date as Megalon, Kenpachiro Satsuma as Gigan, and Tsugutoshi Komada as Jet Jaguar.

Godzilla vs. Megalon was released theatrically in Japan on March 17, 1973, it received generally mixed reviews from critics and audiences with criticism of its special effects and use of stock footage in previous Godzilla films. The film was given a theatrical release in the United States during the summer of 1976 by Cinema Shares. Given this release and subsequent home media, the film has become one of the most well-known kaiju films in the United States. The film's popularity might also be a major contributor to Western perceptions of kaiju films as comedic or campy. The film received revived recognition after an appearance on Mystery Science Theater 3000 in 1991.

The film was followed up by the fourteenth film in the Godzilla franchise, Godzilla vs. Mechagodzilla, released on March 21, 1974.