Old Russian Legation(1890) has been attracted public attention in terms of politics and foreign affairs than architectural style because of conditions of location and historical incident. Though it was heavily damaged during the Korean war, and only the tower has been restored, it is very important in architectural history in Korea, because it is the oldest western style brick building which is existing with the old bishop's house in Myeong-Dong. But it has been impossible to reveal exactly the original form as there has been few reliable materials(picture, drawing, document) and it's remains were nearly destroyed owing to development of the surroundings. Recently the decisive document(site outline map) was found, and new research on the architect Sabatine was studied. So I can get into close with the original form by the results. In this study, I tried to conjecture the original form of the old Russian legation(the size, style, plan and indoor space, arrangement of attached facilities) and I checked the location and structure of the room where King Gojong stayed when he took refuge, and the use of the passage in the basement.