Song Joong-ki as Wolf-Boy / Chul-soo

Park Bo-young as Young Sun-yi / Eun-ju

Yoo Yeon-seok as Ji-tae

Lee Young-ran as Sun-yi

Jang Young-nam as Sun-yi's Mother

Kim Hyang-gi as Sun-ja

Yoo Seung-mok as Professor Kang Tae-shik

Shin Bi as Dong-mi

Woo Jung-kook as Mr. Jung

Goo Bon-im as Mrs. Jung

Lee Jun-hyeok as Policeman

Soel Oh-shin as Thug 1 (uncredited)

Han Min-hik as Thug 2 (uncredited)

Chuay Kwong-lak as Thug 3 (uncredited)

Sung Du-hyung as Man in Black Suit 1 (uncredited)

Cha Jong-ho as Man in Black Suit 2 (uncredited)

Seo Dong-soo as Army Colonel (uncredited)

Jung In-gum as (uncredited)

Lee In-ho as (uncredited)

Oh Yeong-seok as Policeman 2 (uncredited)

Ku Lu-han as (uncredited)

Kim Chul-jun as Construction Worker at Market 1 (uncredited)

Park Young-shik as Construction Worker at Market 2 (uncredited)

Kim Seung-hun as Public Official (uncredited)

Koo Kyo-hwan as Drunk Man (uncredited)

Kim Eun-sook as Military Chief (uncredited)

Hong Sung-ki as Acupuncturist (uncredited)

Hung Hi-kwon as Hospital Doctor (uncredited)

Lee Min-woong as Dr. Kang's Assistant (uncredited)

Nam Jung-hee as Dong-suk's Grandmother (uncredited)

Ahn Do-gyu as Dong-suk (uncredited)

Kim Hae-eun as Woman Renting Mr. Jung's Room (uncredited)

Lee Sung-ju as Sun-yi's Son (uncredited)

Jang seo-yi as Sun-yi's Daughter-in-Law (uncredited)

Jo Jae-yun as Sun-yi's Grandson (uncredited)

Kim Jong-goo as Sun-yi's Father (uncredited)

Shin Yeong-cheol as Eun-ju's Boyfriend (uncredited)