Mothra (Japanese: モスラ, Hepburn: Mosura) is a giant divine moth-like monster, or daikaijū, which first appeared in the eponymous 1961 film, directed by Ishirō Honda and produced and distributed by Toho. Mothra has appeared in several Toho tokusatsu films, often as a recurring monster in the Godzilla franchise. She is typically portrayed as a colossal sentient moth, accompanied by two miniature fairies speaking on her behalf. Unlike several other Toho monsters, Mothra is a largely heroic character, having been variously portrayed as a protector of her own island culture, the Earth and Japan. Mothra's design is influenced by silkworms, their imagos, and those of giant silk moths in the family Saturniidae. The character is often depicted hatching offspring (in some cases, twins) when approaching death, a nod to the Saṃsāra doctrine of numerous Indian religions.

Outside of the Godzilla series, Mothra was the central figure of a trilogy of films starting with Rebirth of Mothra (1996). Mothra also appears in American studio Legendary Pictures' Monsterverse series, alongside other Toho monsters like Godzilla, Rodan, and King Ghidorah in the films, Godzilla: King of the Monsters (2019) and Godzilla x Kong: The New Empire (2024).

Though Mothra is generally portrayed as female, male individuals of her species have also been featured in the franchise, including Battra in Godzilla vs. Mothra (1992), Mothra Leo in Rebirth of Mothra and a male Mothra larva who appears alongside his non-identical twin sister in Godzilla: Tokyo S.O.S. (2003).

Mothra is one of Toho's most popular monsters and second only to Godzilla in her total number of film appearances. Polls taken during the early 1990s indicated that Mothra was particularly popular among women who were, at the time, the largest demographic among Japan's movie-going audience, a fact that prompted the filming of 1992's Godzilla vs. Mothra, which was the best-attended Toho film since King Kong vs. Godzilla (1962). IGN listed Mothra as #3 on its "Top 10 Japanese Movie Monsters" list, while Complex listed the character as #7 on its "The 15 Most Badass Kaiju Monsters of All Time" list.

The name Mothra (モスラ) is the suffixation of "-ra" to the English word "moth"; since the Japanese language does not have dental fricatives, it is approximated "Mosura" in Japanese. The "ra" suffix follows the precedent set by Godzilla (Gojira), which in turn is derived from kujira (鯨, "whale"), which serves to indicate the character's enormous size.

Dican International Pictures entitled the movie Godzilla vs. the Thing, probably to avoid legal action from Columbia Pictures, which had released the original Mothra.

Mothra was first conceived in the January 1961 serial The Luminous Fairies and Mothra by authors Shinichiro Nakamura, Takehiko Fukunaga and Yoshie Hotta, who had been commissioned by Toho to write the outline of a future film. The character was further developed by Shinichi Sekizawa, whose experiences of starving in the South Pacific islands during World War II prompted him to envision a movie featuring an island where mysterious events occurred.

In her 1961 debut, Mothra's adult form consisted of a wire-operated mechanical puppet, while the larva was a suitmation puppet operated by six stuntmen crawling in single file. In Mothra vs. Godzilla three years later, the adult Mothra puppet was modified with radio-controlled legs, while the larvae were portrayed via a combination of motor-driven props and hand puppets. The larval Mothra featured in Ghidorah, the Three-Headed Monster remained largely unchanged from its previous appearance, though the color of its eyes was changed from blue to red. The adult Mothra prop featured in Mothra vs. Godzilla was reused in Ebirah, Horror of the Deep, though previous heavy use had dulled its colors, frayed the fur on the head and damaged the wings.