Lee Tae Hwan, who was born in 1995, will be playing the role of 35-year-old Lee Sung Yeon. Lee Sung Yeon is the older brother of Park Seo Joon's character Lee Young Joon, and Park Seo Joon was born in 1988.

In episode 2, there's a photo of Lee Young-joon meeting Barack Obama and Angela Merkel in 2009.

This show marks Park Min Young's first time playing the leading role in a romantic comedy television series.

This show is based on the novel "Why Secretary Kim" by Jung Kyung-Yoon (first published April 3, 2013 by Gaha).

First script reading took place April 10, 2018 at Studio Dragon in Sangamdong, Seoul, South Korea.

Webcomic "Why Secretary Kim" by Kim Young-Mi is also based on the novel of same name. The web comic was first published 2016 via page.kakao.com.