The Doctors

Kim Woo-jin – Lee Hee-young's fiancé (Episodes 15, 16, 18, 20)

Lee Ga-jin – Hye-jung's stepmother and Yoo-na's mother.

Yoo Hye-jung Kal So-won as child Yoo Hye-jung

Jung Yoon-do

Hong Ji-hong Gil Jung-woo as child Hong Ji-hong Lomon as teen Hong Ji-hong

Jung Pa-ran – General Surgery's teacher, Ji-hong's friend and Yoon-do's uncle.

Yoo Min-ho – Hye-jung and Yoo-na's biological father.

Gong Byung-doo – gang boss (Episodes 1, 3–6, 9)

Cheon Soon-hee – Hye-jung's best friend and Seo-woo's friend.

Choi Young-soo (Kang soo's younger brother) (Episodes 17–18)

Choi Kang-soo – Neurosurgery's 1st year resident doctor.

Kim Soo-cheol's friend

Hwangbo Tae-yang – General Surgery's 1st year resident doctor.

Child Yoo Hye-jung

Kim Chi-hyun

Hong Doo-sik – Ji-hong's adoptive father and Gookil Hospital's chairman.

Jo Soo-ji (Episodes 11–12)

Pi Young-gook – Neurosurgery's 3rd year resident doctor and Seo-woo's friend who had a long-time crush on her.

Kim Tae-ho – Gookil Hospital's deputy director and Head of Neurosurgery

Boss's subordinate

Teen Hong Ji-hong

Yoo Byul – 2nd year nurse.

Yoon Ji-young – Seo-woo's mother.

So-ri

Nam Ba-ram – Nam Hae and Nam Dal's father (Episodes 13–15)

Jo In-joo – General Surgery's specialist.

Lee Soo-jeong – youngest gold medalist in archery (Episode 7–8)

Jin Myung-hoon – Seo-woo's father and Gookil Hospital's director.

Hyun Soo-jin – 5th year nurse.