Mothra (Japanese: モスラ, Hepburn: Mosura) is a fictional monster or kaiju, that first appeared in the 1961 film Mothra, produced and distributed by Toho Studios. 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 larva (caterpillar) or imago, 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.

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. 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.

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, and a male Mothra larva who appears alongside his non-identical twin sister in Godzilla: Tokyo S.O.S.