12 oz. Mouse is an American adult animated television series created by Matt Maiellaro for Cartoon Network's late-night programming block, Adult Swim. The series revolves around Mouse Fitzgerald, nicknamed "Fitz" (voiced by Maiellaro), an alcoholic mouse who performs odd jobs so he can buy more beer. Together with his chinchilla companion Skillet, Fitz begins to recover suppressed memories that he once had a wife and a child who have now vanished. This leads him to seek answers about his past and the shadowy forces that seem to be manipulating his world.

In producing the series, Maiellaro crudely designed the characters as a cost-cutting measure; the series was originally animated by Radical Axis. He intended for the series to lack continuity starting from the pilot but established a serial format after starting the second episode. He had constructed an ending for the series as well as a detailed map of characters; however, the series finale concluded differently from planned. Maiellaro cast people around his office for the characters, starring himself as the protagonist and Nine Pound Hammer vocalist Scott Luallen as the voice of Roostre; the band also performs the opening theme.

The pilot episode for 12 oz. Mouse, "Hired", premiered on June 19, 2005. The series became a regular staple of Adult Swim's lineup on October 23 of that year and originally ended on December 17, 2006. A stand-alone webisode was released online on May 16, 2007. Critical reception was mixed; some praised the series' experimental nature, while others felt confounded by it.

In 2018, a double-length special, entitled "Invictus", aired on October 14 and it was announced that 12 oz. Mouse was also revived as a series. The third season, consisting of 11 episodes, premiered on July 20, 2020, and ended on July 31. The ending credits of both "Invictus" and the season 3 episodes feature a song by Amaranthe and animation by Awesome Inc.

In February 2021, it was revealed that the show would not be picked up for a fourth season.