The development of Information & Communication Technology is contributing to fulfill human desire to improve the quality of life. The quality of human life is realized by actively considering qualitative factors beyond quantitative improvement, and in this process the development of information technology and science plays an important role. The government is trying to improve the quality of human life by solving problems of traffic, communication security, health, and environment in the city through smarter management. Smart city is exposed to a variety of risks arising from environments such as location, conditions, circumstances, and infrastructure, and these risks result in different levels of people s satisfaction with quality of life. Therefore, this study suggests a method of selecting the optimal smart city considering various risk factors of smart cities. The risks arising from smart cities have qualitative as well as quantitative characteristics. Since it is very difficult to objectively evaluate the ambiguity of the qualitative risk, this study selects the optimal smart city considering the ambiguity of risk. This paper presents two goals. The first is to systematically present the risks that occur in smart cities, and the second is to find the optimal smart city by applying the Grey theory to objectify the ambiguity of risk