This paper analyzes the effects of adoption of the International Financial Reporting Standards (IFRS) on the information usefulness of operating income disclosed in the consolidated financial statements over three distinct periods around the adoption of the IFRS. Before 2011, all items in the financial statements including operating income were prepared in accordance with the Korean Generally Accepted Accounting Principles(K-GAAP) in Korea. In 2011, Korea adopted the IFRS. While the IFRS permit a firm to choose the components of its operating income, it could cause the use of different methods for preparing operating income and possibly decrease the comparability across the firms. In order to prevent these issues, Korean Accounting Standard Board(KASB) decided in 2012 to return to the K-GAAP which required for firms to use a uniform method on preparing operating income. As a result, the reported operating income in the consolidated income statements was based on the IFRS only in 2011 and on the K-GAAP in all other years. Due to the unique nature of reporting operating income in Korea, several studies examine the differences in the value relevance of reported operating income based on IFRS in 2011 and that of restated operating income based on the K-GAAP in other years. However, most of these studies mainly focus on operating income presented in the individual financial statements or in the auxiliary financial statements named separate financial statements. Although consolidated financial statements have become the main financial statements since the adoption of IFRS in 2011, no study examines the informational effects of operating income disclosed in the consolidated financial statements under the two different accounting standards. The purpose of this paper is to fill this gap by addressing the question on whether changes in accounting standards affect informational usefulness of the consolidated operating income from the perspective of market participants. Specifically, we collect non-financial firms listed in the Korean Stock Exchange(KOSPI sample) and the Korean Securities Dealers Automated Quotations (KOSDAQ sample), and analyze the relative value relevance of consolidated operating income over three periods around the adoption of the IFRS in 2011: pre-IFRS(2009-2010), IFRS (2011), and post-IFRS(2012-2013). We hypothesize that the reported operating income in the consolidated financial statements based on the IFRS in 2011 is expected to have lower value relevance than that based on the K-GAAP either in the Pre-IFRS period(Hypothesis 1) or in the Post-IFRS period(Hypothesis 2). We also investigate whether the relative value relevance of consolidated operating income is different between two periods based on K-GAAP by constructing Hypothesis 3 that consolidated operating income reported in the Post-IFRS is expected to be more value relevant than that in the Pre-IFRS period. To test the hypotheses, we use the un-deflated price level model by Ohlson(1995) as well as the deflated price level model by previous year stock price, which controls for heteroscedasticity and scale effects. To summarize the results, we find a significant difference in the results across the models, which implies that the results may be affected by heteroscedasticity as well as scale biases from Ohlson’s un-deflated model due to amount variables(Kothari and Zimmerman 1995; Easton and Sommers 2003). In the main analysis, the results based on the deflated model are consistent with our prediction in Hypothesis 1, but not with Hypotheses 2 and 3. Thus, the consolidated operating income reported under the K-GAAP in the Pre-IFRS period is more value relevant than that under the IFRS in the IFRS period, suggesting that allowing discretion in choosing the components of operating income may have deteriorated the informativeness of operating income. Meanwhile, when we examine the KOSPI and KOSDAQ samples firms separately, we observe conflicting evidence. Results based on the KOSPI sample are consistent with our prediction in Hypothesis 1 while being contradictory to Hypothesis 3. In contrast, only Hypothesis 3 is supported in the KOSDAQ sample. Hence, the relative value relevance of consolidated operating income of KOSPI firms(KOSDAQ firms) has been impaired(improved) after the adoption of the IFRS in 2011. These mixed results seem to be attributed to a difference in corporate governance structure between KOSPI and KOSDAQ. Our findings can contribute to the extant accounting literature by providing evidence which the KASB and regulatory authority may consider in implementing the accounting standards and policies.