This study aims to develop an understanding of how circular economy should be implemented to result in sustainable development and to analyze the potential of one particular implementation to result in sustainable development. “The sustainable development way of implementing circular economy” is presented by understanding circular economy with system thinking and considering the factors affecting the implementation of circular economy. Interviews and text-analysis are conducted to analyze the character and potential of ReTuna, a reused items mall in Eskilstuna, to result in sustainable development. Results show circular economy should be implemented as a way of reasoning that can result in a systemic transformation of the economic system to result in eco-centric sustainability. Implementations that do not explicitly derive from a an understanding of circular economy as a new way of reasoning are despite this valuable due to a system’s character of interconnectedness. ReTuna is implemented as a set of practices and an organizational structure but it also demonstrates an honorable effort to change people’s perception of the human-nature relationship. It is concluded that way of implementation has to reflect and be synchronized with the aspiration behind implementing circular economy. ReTuna has potential to result in sustainability but does not yet.