 In 2003, Jeong and her costar Kim Rae-won rose to fame with "Cats on the Roof".Depicting a boy and a girl platonically living together then falling in love (with cohabitation at the time a taboo topic in the South Korean mainstream), the series was a smash hit, especially popular among teenagers and twentysomethings.Jeong became known for her cheerful and positive image, and in 2004 she headlined her first film, the romantic comedy "He Was Cool" opposite Song Seung-heon, based on the internet novel by Guiyeoni.