This paper discusses house types and their transformation of Fuzhou city in Fujian（China）. Authors selected the old castle district of the central part of Fuzhou, which are called Sanfangqixiang and Zhuzifang at present, as an intensive field study and clarified the typology of dwelling units and the transformation process. The central areas of old castle are still occupied by low rise houses and shop houses and are designated as a preserved area. The formation of the target areas, the origin of which goes back to Tang dynasty, does not seem to follow a certain formal system, but we can point out the system of formation of street blocks, based on typology of traditional house dacao
and its collective form. This paper classified 39 residences called dacuo , which we measured and collected from the others' documents, in terms of the numbers of spans and courtyards, into several types and discusses the collective systemof dacuo.