Park Sieun (박시은) is a South Korean actress and singer. She is a member of the girl group STAYC. She made her acting debut in 2014 as one of the main characters in the children's television series Pluto Secret Society. Her father is singer Park Nam Jung. On January 18, 2017, it was announced that Park had signed a contract with JYP Entertainment. She left JYP Entertainment and is now under High Up Entertainment. After signing with High Up Entertainment, she debuted as a member of the girl group STAYC in November 2020.