The purpose of this research is to help outdoor space planning reflected real needs of apartment residents in the differentiation elements of outdoor space, by using USC trade-off game in three apartment complexes in Seoul. This game method was used to evaluate their preference, reliability of preference degree, satisfaction degree, requirement elements such as improvement, sacrifice, maintenance of present condition, and payment possibility for improving and maintaining present condition, in addition to their preference and payment possibility of differentiation of outdoor space in the apartment complex in the future. From the statical analysis, we found the following results: 1. Reliability of preference degree was valid, inasmuch as the first elements they preferred were the almost same as the last things. 2. Elements of preference were pedestrian ways, pedestrian security facilities, various athletic facilities, and variety and high-class facilities in a play ground. 3. Satisfaction degree of differentiation elements of outdoor space was low not only in total complexes but also in each complex. As a result of analysis, these elements were not satisfied with residents. 4. Most of the differentiation elements of outdoor space in three apartment complexes, except planting traditional trees, were required to improve and maintain present condition. The cost to improve and maintain these elements able to pay by them was about 2.18 million won. Through this result, these elements were not options but prerequisites for planning outdoor space in apartment complexes. 5. In the future preference elements of differentiation of outdoor space in apartment complexes were pedestrian and jogging ways, places with water, various athletic places and facilities, multi-function resting places, green spaces in experiences, pedestrian security facilities, various athletic facilities, variety and high-class facilities in a play ground, and payment possibility for these elements was about 3.20 million won.
