Drawing largely upon the stakeholder theory and the resource dependence literature, this article examines the relationship between corporate governance structure and sustainability measured by energy efficiency. The model uses data from South Korean (Korean hereafter) firms that have relied heavily on energy- intensive industry for economic growth and have experienced major changes in their corporate governance structure since the 1997 Asian financial crisis. Estimation results show that a corporate governance structure that includes the appointment of heterogeneous outside directors, given other conditions, leads to an increase in energy efficiency and thus sustainability.