The missionary work started by the missionary Harace Allen in 1885 has been expanded in all directions through the activities of the Chaplain's Office. Accordingly, the Chaplain's Office plays an important role as a center of the missionary work of this hospital and as the forerunner of pastoral duties.

For the new vision of the 21st Century, Yonsei University Health System (YUHS) is preparing a place for holistic treatment through spiritual treatment in this country by educating and training hospital pastors in Korea.

With these motives and goals, the Chaplain's Office progresses every observance in the hospital based on Christianity according to the office regulation (Article 4, Chapter 4) of the YUHS which states, "The Chaplain's Office preaches the Christian Gospel to the faculty, medical students and patients, and takes charge of its related general administrative affairs". The office carries out pastoral duties at four levels; for students, school staff, patients and education.

In 1993, Yonsei University Health System(YUHS) initiated medical missionary activities for Mongolia in celebration of the centennial anniversary of the arrival in Korea of Dr. Oliver Avison, the founder of this medical college.

YUHS established a sisterhood relationship with Mongolia National Medical College on March 24, 2003, and formed an agreement to hold scientific interchanges, medical support and medical seminars. Since then, YUHS has been continuing with the operation of various programs including a professor exchange program of the medical school, Mongolian professor training-program, medical consultation services, and the opening of a friendship hospital, Yonsei Memorial Library, central laboratory, and Lee Tae-joon memorial park. In January 2001, a proposal associated with the establishment of the medical missionary work center was passed by the foundation board of directors and this center started functioning as a regular organization to take full charge of all medical missionary activities in March of that year.