This research work is to analyze architectural characteristics of Sungnyemun especially in King Yeongjo's reign in Joseon dynasty. The result of this research is summarized as following: 1. The architectural characteristics of Sungnyemun in King Yeongjo's reign are closely related with Confucian ceremonies such as Jeon-jwa and Heon-goek-rye. To perform these ceremonies, some lower walls of Sungnyemun's wooden pavilion were removed and used as ceremonial space. And after ceremony it was restored. 2. The floor type of center bay of the 1st story of wooden pavilion should have a type of floor using long and narrow fine tree plate, which is same type before the repair work of 1960's dismantlement. 3. The width of east stairway which is reached to east small gate, was changed just before Japanese's rule(1910～1945), should be broaden than present width, which is proven through the recent excavation. 4. The reason of asymmetric characteristic of locations of both east and west narrow-gate, and widths of east and west stairway, are related with order of King's ceremony.

The Great south gate of Seoul Castle, Sung-Rye-Mun, the east gate of Seoul Castle, Hung-In-Ji-Mun, the south gate of Hwa-Sung Castle, Pal-Dal-Mun and the north gate of Hwa-Sung Castle, Jang-An-Mun are typical significant castle gate of Chosun Dynasty. They have a lot in common with exterior. Additionally there are also something common in dimensions. At first, the arch dimensions of lower story is very similar and the columns of upper story are the regular intervals. Purpose of this study is to confirm similarities above mentioned were intended on purpose and if then what was the reason. The results of this study were described separately as follows. 1. The widths of the arches were based on each 16Cheok and 18Cheok. 2. The heights of the arches followed less strictly rule than the widths. 3. The widths of the arches, 16Cheok was same size as width of middle-size road (中路, Jung-Ro) inside the Castle town in Chosun Dynasty. 4. The widths of the arches, 16Cheok was the standard size of exit went through castle and then the standard size of road arrived at one's destination. 5. The widths of the arches had an effect on the intervals between the columns of the upper story. Finally we recognized that in Chosŏn Dynasty the widths of the gate arches in Seoul castle and Hwa-Sung castle had relevance to the city planning largely and widths of the gate arches had an effect on the intervals between the columns of the upper story partly.