Sustainability assessment systems are commonly used to achieve sustainability. However, internationally agreed systems are difficult to locate. Analysis of sustainability assessment systems in various contexts can lead to creating a standardized sustainability assessment framework. Here, we reviewed the experience of the sustainability assessment system applied in Korea for sharing knowledge and providing implications for creating internationally standardized sustainability assessment frameworks. The subject of the study was the assessment of sustainability of cities (ASC, conducted annually by the Korean government) using data from the 2015 assessment and consisting of two parts: Descriptive analysis of the ASC system and analysis of the 2015 ASC assessment results. The ASC assessment unit is the low-ranked municipality, and indicators include social, economic, environmental, and institutional themes. The ASC assesses overall sustainability by incorporating mandatory and voluntary indicators, and the Korean government encourages improved sustainability through awards, diagnostic reports, and incentives. Gun was highly evaluated in social sustainability, and the southern Seoul metropolitan area and Chungcheong area were highly evaluated in economic sustainability. In environmental sustainability, metropolitan cities received high scores, while institutional theme scores were not high in any specific area. Municipalities in metropolitan cities received higher voluntary indicator scores than rural areas.