In the modern era where corporations form the foundation of national economic activity and serve as major economic agents, accounting information related to corporate management activities is an important decision-making tool. In particular, accounting earnings provide not only information for firm valuation that determines stock prices but also information on stewardship responsibility that determines managerial performance evaluation and compensation. However, because accounting earnings are measured based on historical cost and conservatism principles, questions have been raised about how useful accounting earnings are for information users' decision-making. In particular, under rapidly changing business environments and fiercely competitive investment conditions, agency problems due to decision-making uncertainty and information asymmetry have been significantly amplified. To address these problems, an increasing proportion of firms are using non-financial performance measures and undisclosed internal performance measures for firm valuation and managerial performance evaluation. Due to these changes in the accounting environment, criticism of the information usefulness of accounting earnings (value relevance and stewardship relevance) has intensified. This study recognizes the issues regarding the information usefulness of accounting and aims to analyze the information usefulness (value relevance and stewardship relevance) of accounting earnings using time-series data spanning the past 20 years for Korean firms. In particular, it seeks to examine how information usefulness changes with shifts in the accounting environment by decomposing accounting earnings into their major components: cash flows and accruals. The results of this study are as follows. First, although there is a theoretically positive relationship between value relevance and stewardship informativeness of accounting earnings, this direct relationship was difficult to verify in the empirical analysis. Second, the time-series decline in the valuation informativeness of accounting earnings was far more severe than the time-series decline in stewardship informativeness. This implies that even if the valuation informativeness of accounting earnings decreases over time, the stewardship informativeness of accounting earnings does not decrease at the same rate—meaning that differences in informativeness exist across the different roles of accounting earnings. Third, the deterioration in the information usefulness of accounting earnings was empirically found to be related to the persistence of corporate earnings.