Ko Ah-seong is a South Korean child actress.
Already established as a star in children's entertainment, Ko made her film debut in 2006 with a starring role in The Host, having been cast in an extensive audition process. The films director, Bong Joon-ho
, praised her work, saying that she "showed really mature acting for her age, and that's one of her defining charms as an actress". Ko was also applauded by film critics, with Stephen Hunter of The Washington Post complimenting her "exquisite performance", and Megan Ratner of the Bright Lights Film Journal noting her "unforced naturalness, reminiscent not only of Ana Torrent but of Zazie’s Catherine Demongeot". She has received several award nominations for her role in the film, and won "Best New Actress" at the 2006 Blue Dragon Film Awards.
In 2007 she appeared alongside Jeong Jin-yeong in the film The Happy Life.