Y:SY
- Born
- 22 January 2000 (26 years)
- Place of birth
- Seoul, South Korea
- Gender
- Female
Lee Seo-yeon, known professionally as Y:SY, is a South Korean singer-songwriter and rapper under H1GHR Music. She is a former member of the girl group fromis_9, formed through the reality survival show Idol School (2017). She left the group in 2024. She made her solo debut on November 17, 2025, with the digital single Naked.
