Are smart cities sustainable? This study aims to seek how the concepts and applications of the smart city and the sustainable city can be integrated. Smart city policy practices tend to principally focus technological or economic aspects. However, superficial application of cutting-edge information communication technologies or the internet of things may not transform the city into a place for better quality of life and co-existence with the ecosystem. The sustainable smart city framework that combines sustainability (economic, environmental, and social) pillars with good governance can provide commonly shared visions and practices for urban development. However, an empirical assessment of the Korean Smart City Act suggests that current policies focus more on economic and technological benefits from implementation of smart cities. Environmental and social research and practice require mainstreaming of seemingly neglected components of sustainability for current and future urban policy formation.