Background: The average hospital stay in most Korean teaching hospitals is longer than that of hospitals in developed countries. The investigation of average hospital stay of teaching hospitals is considered as an important measure to evaluate the effectiveness of hospital management. In this article authors analyzed the relationship of several variables (hospital ownership, number of beds, location of hospitals, number of physician) to length of hospital stay in each clinical department. Methods: The average hospital stay of each clinical department of 184 teaching hospitals was investigated. Authors reviewed the papers of teaching hospitals, that was reported to the Korean Association of Hospitals. Results: The means of hospital stay day of hospitals were not significantly different according to the number of hospital beds and location of hospitals. Only the difference of hospital stay according to ownerships was significant. The length of stay was the highest in public hospitals and the lowest in juridical hospitals. Conclusions: The number of beds and location of hospitals were not associated with the average hospital stay. But ownerships affected the average hospital stay. The national or public hospitals had the longest length of hospital stay. Number of specialists and number of all physicians were closely related to the average hospital stay.