Purpose: This study aims to explore an one-year experience of intensive core clinical clerkship (student internship, subinternship) in Gachon Medical School for junior clinical students, and the immediate outcome of the program was discussed along the with advantages and student load. Methods: 36 junior medical students (M5) were exposed to 36 weeks of core clinical clerkship including internal medicine (12wks), pediatrics (6wks), obstetrics-gynecology (6wks), general surgery (4wks), psychiatry (4wks), and emergency medicine (4wks). The clinical service team was made of faculty member (1), senior resident (1), intern (1) and M5 students (1-2), and the students who were involved a wide range of baseline responsibilities corresponding to those of regular rotating interns. They were encouraged to participate the various procedures and decision making process, but their participation was restricted by keeping 3 levels of performance policy according to degree of supervision. Questionnaire analysis was carried out immediate after the student internship. Results: Students were proud of themselves being as the subinterns and showed a strong motivation, while they had a difficulty to tolerate a strong psychologic pressure by taking their roles of subinternship. Major responsibilities of clerkship were focused on the clinical information collection (history taking and physical examination), students-directed group conference, faculty-led small group discussion, technical skill learning and ward round in order. Students appreciated well to this internship in terms of acquisition of clinical skills and identification of their role, but shortage of space, frequent on-call, lack of self-directed learning opportunity, unclarified requests from the hospital authority were pointed out. Conclusion: It is assumed that student internship is a strong tool to promote the quality of clinical learning process, but requires details of teaching instructions(manuals) aside from solving a series of legal on malpractice, for which critical defining of clinical participation is essential to upgrade the Korean version of clerkship.