The single-family detached houses, built in the early 1970s at Kangnam in Seoul, have been transformed into three to four story multi-family houses and mixed used complexes for the last 40 years. The paper examines how the residential areas at Kangnam have been commercialized and how urban architecture has been replaced and changed. Fourteen buildings within three large urban blocks at the center of Kangnam-gu were selected and analyzed. It was discovered that the average lot size of the these buildings is 310 square meters, which is about twice the residential areas planned at Kangbuk with the same city planning method in the same period. The average area per floor is 152 square meters; average total floor area is 578 square meters; and average height is 4 stories with basement. The transformation could be classified into four types: the horizontally and vertically expanded single-family house (T1); the single-family house partly modified for office functions (T2); the rebuilt medium-sized multi-family house and row house (T3); the four to five story commercial complex (T4). The paper also discovers that the office and retail spaces penetrated into the houses are interrelated to the medium and small sized specialized service industries at each block respectively. The paper argues that the continuous urban studies with the theoretical frameworks encompassing economic and socio-cultural perspectives are required for exploring new urban architecture in the rapidly changing Seoul.