Supporting
Kim Ji-won as Yoo Rachel
Kim Tan's fiancée. The rich, chic and haughty heiress of clothing company RS International, she is also known as the "Paris Hilton of Jeguk High School". She dislikes Cha Eun-sang, and attempts many times to split her and Kim Tan apart. She is also on close terms with Tan's half-brother, Kim Won.
Kang Min-hyuk as Yoon Chan-young
Son of Jeguk Group's secretary. Kind, cool-headed, warm, and smart, Chan-young always sees the best in people. Despite being in the social care group, he doesn't get picked on by the "higher social status" students because he is the class president. He is also Eun-sang's best friend, and his friendship with her makes his girlfriend, Lee Bo-na jealous. Nonetheless, Chan-young thinks that everything Bo-na does is cute, especially when she is jealous.
Krystal Jung as Lee Bo-na
The beautiful daughter of the CEO of Mega Entertainment. Though somewhat spoiled, she is actually kind-hearted. She is praised for her beauty and cuteness. She is Kim Tan's first love and ex-girlfriend, and now they are still on friendly terms. She is now dating Chan-young. She dislikes Eun-sang at first for being Chan-young's best friend, believing that "there is no way for a girl and a boy to simply be just friends", but as the time goes by she became friends with her. She has a protective older brother she is close to who studies in New York.
Kang Ha-neul as Lee Hyo-shin
Son of the attorney general. Calm and laid back, he runs the school broadcasting system together with Bo-na and later Eun-sang. He is also close friends with Kim Tan. Hyo-shin is constantly pressured by his family to get into law school, despite his dislike for the profession. To overcome his family's pressure, he joins the army without telling anyone besides Tan and Rachel. Hyo-shin also has a one-sided crush on his private tutor, Jeon Hyun-joo, but later falls for Rachel.
Park Hyung-sik as Jo Myung-soo
Son of the CEO of Victory Law Firm, the largest law firm in the country. He is quick-witted, playful and often jokes around. He often hangs out at nightclubs and takes photos of his friends. He is best friends with Young-do and Bo-na.
Jeon Soo-jin as Kang Ye-sol
The daughter of a former bar hostess who owns 10 large bars in Gangnam. She is Lee Bo-na's best friend. Her existence in Jeguk High School was unremarkable until Rachel exposed her mother's profession, which temporarily halted her friendship with Bo-na as she had looked down on Eun-Sang for her humble upbringing despite her own mother's past profession as a bar hostess. She has a crush on Choi Young-do.
Cho Yoon-woo as Moon Joon-young
A victim of Choi Young-do's bullying at Jeguk High School due to his "welfare status". He later leaves the school.
Choi Jin-hyuk as Kim Won
Kim Tan's older half-brother. The son of his father's first wife, who died when he was young. He is an accomplished and capable young executive who runs his family's giant conglomerate. At constant friction with his family, he attempts to rule the company himself, and fears that Tan will get in his way. Due to this, he had never had a real brotherly relationship with Tan, despite the latter trying everything he can to win his brother's heart. He is in a relationship with Hyun-joo, whom he later gives up on for the sake of the company.
Jung Dong-hwan as Kim Nam-yoon
President of Jeguk Group, and father of Kim Tan and Kim Won.
Kim Sung-ryung as Han Ki-ae
Kim Tan's mother and the mistress of Kim Nam-yoon. Though somewhat vain and self-centered, she cares for her son deeply and only wants him to be happy. She later forms a friendship with Eun-Sang's mother.
Park Joon-geum as Jung Ji-suk
Chairwoman of Jeguk High School. Kim Nam-yoon's second wife, and Kim Tan's legal mother. Selfish and controlling, she attempts to take over Jeguk Group when her husband falls ill.
Kim Mi-kyung as Park Hee-nam
The mute housekeeper of Tan's family, and mother of Eun-sang. She lost her voice when she was three years old due to a severe fever. She often gives advice to Kim Tan's mother. She is kind, and wants the best for her daughter.
Choi Won-young as Yoon Jae-ho
Jeguk Group's secretary and Chan-young's father, who was previously involved with Esther Lee. He is Kim Won's confidant.
Choi Jin-ho as Choi Dong-wook
President of Zeus Hotel Group and father of Young-do. He is controlling and violent, and became a womanizer after his first wife, Young-do's mother, left their family. He is engaged to Esther Lee, but he's having an affair.
Yoon Son-ha as Esther Lee
President of RS International and Rachel's mother, who is engaged to Choi Dong-uk, Young-do's father. However, she still appears to be in love with Yoon Jae-ho, whom she previously gave up on to marry someone who would help her business.
Lim Ju-eun as Jeon Hyun-joo
A teacher at Jeguk High School. Diligent and earnest, Hyun-joo gets Kim Won's attention for her sharp intelligence, and they enter into a relationship. But she eventually broke up with Won to allow him to concentrate on running the company. She is also the private tutor of Hyo-shin, who had a crush on her.
Baek Seung-hyeon as Secretary Jung
Choi Ji-na as Yoo Kyung-ran
Choi Young-do's mother.
Seo Yi-sook as Lee Hyo-shin's mother
Jung Won-joong as Lee Chan-hyuk
Lee Hyo-shin's father.
Lee Yeon-kyung as Lee Bo-na's mother
Ra Mi-ran as Jo Myung-soo's mother
Choi Tae-hwan as Lee Sang-woo
Choi Young-do's lackey.
Yang Seung-pil as Hyo-joon
Choi Young-do's lackey.
Kang Kyung-hun as Dong-wook's lover
Choi Eun-kyung as Kang Ye-sol's mother
Hwang Young-hee as Jeguk High School teacher
Lee Joon-woo as student
Lee Ga-ryeong as clothing store employee
Jung Da-eun as herself
