As the economy and society grow and environmental pollution and social problems emerge, firm’s interest in ESG and sustainable management is increasing. Against this background, corporates are making efforts to disclose their ESG activities, and the government is moving to establish standards and obligations for corporate ESG disclosure. In order to give justification to ESG activities, academia is conducting research to reveal the effect of ESG activities on performance. Therefore, this study analyzed the effect of ESG on management efficiency. For this, the ESG grade of the Korea Corporate Governance Service, DEA, and Tobit regression were used. As a result of the analysis, it was found that the higher the ESG grade, the lower the management efficiency. This negative (-) relationship was moderated in the positive (+) direction as the firm size increased. This means that ESG activities can be negative in terms of efficiency. It also indicates that the impact of ESG may vary depending on the characteristics of the corporate. This study has academic implication in that it extends ESG-related research to the aspect of efficiency. In addition, it has practical implications that factors to consider are provided to policy makers and corporate decision makers.