Um Ki-joon (Korean: 엄기준; born March 23, 1976) is a South Korean actor. He made his acting debut in 1995 in the stage play Richard III, though he later became best known as a musical theatre actor, starring in Singin' in the Rain, The Sorrows of Young Werther, Grease, The Three Musketeers, Jack the Ripper, The Count of Monte Cristo, Catch Me If You Can, and Rebecca. He also appeared in the Patrick Marber play Closer.

Um's popularity increased after he began playing supporting roles in television dramas such as Life Special Investigation Team, Worlds Within, Hero, Dream High, Scent of a Woman and Phantom. He was also the leading actor in Good Job, Good Job and The Virus. He is best known for his roles in television series I'm Not a Robot (2017–2018), The Penthouse: War in Life (2020–2021) and Little Women (2022).