The purpose of this research was to analyze the correlation of residential satisfaction and the size of housing unit in apartment housing through the case study of 1,619 samples of 36 housing estates. The contents of this research consisted of two main parts. The first part was to identify the differences of residential satisfaction of dwellers, based on the size of housing unit, in apartment housing. The second part was to analyze the characteristics of residential environment, which might have an influence on the differences of residential satisfaction. the findings of this study were that the residential satisfaction of dwellers was proportional to the size of housing unit except $39m^2$ under housing unit, and the size of housing unit was not proportional to the residential satisfaction of outdoor openness exactly, but the size of housing unit was proportional to increase of the distance between building and building, and decrease of the building surface coverage ratio to outdoor area. This research will contribute to the establishment of the site planning methods which increase residential satisfaction in apartment housing, while promoting the quality of residential environment in Korea.