The purpose of this study is to examine the relation between operational efficiency and earnings quality. We construct a quantitative non-financial indicator of operational efficiency using Data Envelopment Analysis (DEA) based on a vector of firms’ inputs and outputs to estimate the relative efficiency of firms in an industry. Empirical tests are conducted for non-financial firms listed on the Korea Stock Exchange for the period 2002-2012. The results of our study are summarized as follows: Using two alternative earnings quality measures (earnings persistence and accruals quality), we find that higher operational efficiency is associated with higher earnings quality. This result shows that earnings of firms with high operational efficiency have ability to predict future earnings, which implies that operational efficiency plays an important role in predicting a firm’s future earnings. Also, it indicates that high operational efficiency mitigates the possibility of earnings management. The prior research has mainly adopted simple ratio analysis (e.g., return on investment) to compute proxies for efficiency to explore the relation between efficiency and firms’ earnings quality. The simple ratio analysis has limitations in reflecting firms' production function with multiple inputs and outputs. DEA is a non-parametric method that uses multiple inputs and outputs to measure the relative efficiency of DMUs and implicitly allows for differential weighting among inputs, which should provide a more comprehensive and precise measure of a firms’ operational efficiency than simple ratio analysis. While the prior research has used rank-variables, change-variables and dummy-variables as proxies of efficiency measure, we employ level-variables and therefore, we provide more clarifying result and sophisticated analysis. Furthermore, we present technical efficiency as well as pure technical efficiency and scale efficiency, which provide various analysis results. The majority of prior research has measured efficiency and focused on investigating the cause of inefficiency. Whereas, this study provides empirical evidence on the usefulness of operational efficiency by examining the association between earnings quality and operational efficiency. Our results can help accounting researchers and investors predict firms’ future earnings by providing evidence and methodology on how to use information about operational efficiency.