This study mainly examined the unit space (room) called 'MARI' of the private houses that were built between the 19c and the early 20c in the insular areas of southwestern sea. Generally, this region has unique historicity (restructure of the insular environment in the 17c and the 18c) and geographic environment that are different from inland regions thus the environment is presumed as a related factor to developments and structures of the private houses. 'MARI' is a noticeable space that is installed in a main building without an exception even in small 3 bedroom private houses. Its nature has location and usage distinctions in an architectural plan with similar 'MARU' of inland Jeollanam-Do. There are large crocks filled with grains at MARI. Thus, MARI is a storage room. Mostly rice and various other kinds of grains are stored in the several crocks, large and small. Many household goods are kept here as well. Another peculiar function of MARI is that this space commonly enshrines ancestral tablets of three generations. Hence, MARI takes a role of a shrine of an aristocratic house from an inland region. Considering the size of the house and space, this seems to be a very unprecedented utilization of area. MARI is located at the top (at the head of the house) on the floor plan. In other words, it is located at the space in the highest rank. The importance of ancestor worship and grains is evinced architecturally. It is really interesting fact that MARI is also located within recently built modern houses (Cheongsan Island, Joyak Island, etc.). Therefore, it can be said that the unique MARI tradition of this region has an intact continuity even today. After all, MARI has a great significance as a unique unit space of insular areas of southwestern sea that is installed in the main buildings of all houses regardless of size and shape of the houses, and their insular locations.