<![CDATA[Earnings quality represents a central attribute of financial reporting that determines the reliability of stakeholder decision-making, yet empirical evidence on its determinants remains inconclusive, particularly in the basic materials sector. This study examines the effects of capital structure, profitability, and accounting conservatism on earnings quality, with the investment opportunity set (IOS) as a moderating variable, among basic materials sector manufacturing companies listed on the Indonesia Stock Exchange during 2022–2025. A quantitative approach was employed using secondary data from annual financial reports, with a final sample of 80 companies yielding 320 firm-year observations selected through purposive sampling. Data were analyzed using panel data regression and Moderated Regression Analysis (MRA) with EViews 14, following selection of the Common Effects Model through the Chow, Hausman, and Lagrange Multiplier tests. The results show that capital structure and profitability do not exert a significant effect on earnings quality, whereas accounting conservatism has a positive and significant effect. Regarding the moderating role of IOS, the investment opportunity set does not moderate the relationship between capital structure and earnings quality, but significantly moderates the relationship between profitability and earnings quality. These findings indicate that earnings reliability in the basic materials sector is primarily driven by the consistent application of the prudence principle and the interaction between profitability and growth opportunities, rather than by capital structure composition alone. This study contributes to the financial accounting literature by providing early empirical evidence of IOS as a moderating variable within an integrated framework applied to the Indonesian basic materials sector.]]>
