This study attempts to analyze the ecological characteristics of apartment houses’ interior designs that more than 50% of Korean people live in and to suggest the future direction to improve the quality of residential environments. The research survey included visiting model-houses from June to September, 2006. Among thirty eight construction companies that were selling their apartments in Busan, Korea during 2006, eight companies that distributed large-sized apartments of more than 132m2 through the model-house distribution system were selected. Twenty units shown as full-scale models in the model-houses of these companies available for distribution were analyzed by the ECO-checklist. The ECO-checklist was designed based on the literature reviews of the previous studies in order to analyze the interior environments in ecological aspects. It includes four categories: 1) energy efficiency, including the use of natural and artificial lighting, natural ventilation, and control of heating and cooling, 2) exterior and interior greening, 3) sustainable use of natural resources such as materials and water, and 4) flexibility of space for future use. The following findings have been categorized. First, in terms of energy efficiency, natural lighting and interior ventilation did not show any problem by using an arrangement of south-heading orientation and large-sized sliding windows. Second, for the finishing materials, most of the floors were covered with wood flooring or polished tiles, while the walls and ceilings were covered with silk wall paper. Third, the finding showed that interior greening was considerably insufficient. Verandas in living room or bedrooms were provided for greening and multipurpose use, but actual plantings were few. It would be an appropriate solution if construction companies provide the residents with beautiful and easily maintained tree-planting veranda areas with the proper drainage facilities rather than change the veranda to an extended room area. Finally, in terms of space flexibility, it would be possible to reduce the materials wasted if the spatial configuration can be easily changed in accordance with life span and the needs of the family. However, most of the spaces currently provided are fixed. Through the installation of a flexible wall system that can be easily be moved by ceiling rail, the residents can enjoy the flexibility of the given space and control the number of the rooms according to their needs.