It was in 2005, however, that Kang established herself as a star outside of her appearance in Oldboy. The sharp-edged relationship drama Rules of Dating, in which she starred opposite Park Hae-il, proved to be an unexpected hit, and then two months later she took a small but central role in box office megahit Welcome to Dongmakgol. In a 2005 survey of influential movie producers, she was ranked among the top ten most bankable stars.