Lycanthrope Leo (Japanese: 烈王（レオ）, Hepburn: Reo) is a Japanese manga series written by Kengo Kaji [ja] and illustrated by Kenji Okamura [ja]. It was serialized in Shogakukan's seinen manga magazine Young Sunday from 1991 to 1993, with its chapters collected in four tankōbon volumes.

Written by Kengo Kaji [ja] and illustrated by Kenji Okamura [ja], Lycanthrope Leo was serialized in Shogakukan's seinen manga magazine Young Sunday from December 27, 1991, to September 10, 1993. Shogakukan collected its chapters in four tankōbon volumes, released from July 4, 1992, to November 5, 1993.

In North America, the manga was published in an American comic book format by Viz Communications, with seven issues released in 1994. It was later published in graphic novel format; however, it was canceled after releasing one volume.