Seo Yi-sook (born December 6, 1966) is a South Korean theatre, television and movie actress. She is a recipient of the 2003 Gu Hi-seo Theatre Award for Actor of the Year and Expected Actor, the 40th Dong-A Theatre Award for Best Acting (2004),[5] and the 30th Lee Hae-rang Theater Award (2020).[6]

Seo began her career in 1986 by joining a local theater company in Suwon. She received the Best New Actor Award at the 1986 Korea Theatre Festival and an Acting Award at the 6th National Theatre Festival in 1987.[7] After joining the Michu Theatre Company in 1989, she made her debut with the company in Shin Yi Gukgi. The following year, she debuted as a musical actress in Make a Hero (1990).

Seo made her first television appearance as a supporting actress in 2010. Her television work includes supporting roles in Empress Ki (2013–2014), The Rebel (2017), Hotel del Luna (2019), The World of the Married (2020), and Start-Up (2020); and also feature film The Mayor (2017).