Mothra resembles a giant, furry, multicolored moth with large blue compound eyes. Instead of a proboscis , like how most adult lepidoptera have in real life, she retains her mandibles from her larval stage.

Her wings are large and have patterns that resemble tribal paintings and lighting, and yellow and orange eye spots near the tips of each of her forewings.

Mothra is an ancient moth goddess that resides on the tropical paradise called "Infant Island". She serves as the guardian of a Earth and nature, as well as a group of natives on the island and has.two tiny twin priestesses called "The Shobijin" (or the "Cosmos" or "Elias" depending on the movie), who serve as her translators to humanity. Mothra is depicted as an immortal deity in most films and despite having died multiple times, she is always reborn through eggs she lays before battle or due to old age. Mothra has protected the planet many times from monsters like King Ghidorah and sometimes has been put in conflict with Godzilla. Other times, Mothra has worked alongside Godzilla in order to fight off alien invasions.

Mothra embodies the nurturing side of nature, and is portrayed as a kind and benevolent creature. She is gentle toward all life, however, her willing to fight to maintain the balance of the planet often comes with destruction of those caught in her battles with other kaiju. Despite this, Mothra is peaceful and only engages in brute force when acting as protector to her worshipers on Infant Island, or as collateral damage while protecting Earth from a greater threat. This peaceful nature was prominent with her counterpart Battra, whom Mothra initially did not want to harm, but was ultimately forced to after Battra's actions threatened all life in Earth.

Mothra has a positive relationship with the Cosmos, who often speak for her. The Cosmos revere both Mothra and Battra as two different divine forces of nature. They act concerned when Battra is injured, and are pleased when Mothra finds a nonviolent method of stopping Battra, "making friends," as they say in the film.

As an adult, her wings can (and generally do) create gales which tear apart buildings and send other kaiju flying. Her great bulk of a body is commonly used to her advantage in battle to slam into opponents (both in larva and adult form), and her surprising levels of strength can help her to drag and even lift monsters like Godzilla.

Mothra is one of the most powerful psychics among the kaiju. She uses this power benevolently, to communicate with humans, or defensively, to destroy her enemies.