This paper aims to clarify the character of mansions built during the Period of the Republic of China in Nanjing, by focusing on spatial composition and the exterior space arrangement of the main building. Based on the historical background of the Republic of China, historical textual research and on-the-spot investigation were carried out into the spatial composition of the mansions, 17 mansions are selected as study objects. Analyzing the two-dimensional composition of sites and the three-dimensional composition of attachments for the main buildings shows the character. The result of this research indicated that, the two-dimensional composition such as the position of mansion on its site, and the three-dimensional composition such as the position or type of attachments, not only imitates European and American residence, but also utilizes characters of traditional Chinese residence. The main building’s position and plane figure of the site on the exterior arrangement, which can be seen as a combination of Chinese style and Western style, has changed.
