The relationship subsisting between board structure of corporate organizations and earnings management has attracted several concerns particularly to regulatory agencies, management, accounting practitioners and researchers alike. Therefore, this study, examined the extent to which board independence and size influence the level of earnings management of publicly quoted Nigerian firms. For this purpose, the adoption of the International Financial Reporting Standards (IFRS) and the age of firms were introduced as mediating variables. Secondary data were however pooled from the financial statements of ninety-two (92) firms cutting across ten (10) industrial sectors from 2007–2018 (12 years). The regression analysis amidst other relevant statistical techniques was adopted to analyze the collated pooled data. Evidence from our result indicates that with the introduction of IFRS adoption and firm age as mediating variables, the Fcal obtained was 1.72 (p-value = 0.1424), thus indicating that the size of boards and the presence of independent directors (board independence) in corporate boards could not significantly influence the level of earnings management in Nigerian firms. We therefore recommend that in order to regulate managements’ opportunistic behavior/earnings management, regulators and stakeholders who are charged with the task of performing oversight functions on the activities of management should lay more emphasis on ensuring that preparers of financial statements fully comply with the provisions of IFRS and other regulatory requirements for financial reporting.