[Purpose] This study investigates the moderating role of CEO ownership in the CSR spillover effect within the context of mergers and acquisitions (M&A). Using M&A as a quasi－experimental setting, it explores how peer pressure from high－CSR acquirers affects firms’ CSR activities. [Methodology] Specifically, this study explores how CEO ownership affects MSCI ESG scores, particularly in response to industry－wide M&A activity by high－CSR acquirers. [Findings] Analyzing 22,271 firm－year observations of U.S. public firms, this study reveals that CEO ownership significantly influences the CSR spillover effect. Firms with high ownership CEOs are less likely to emulate the CSR practices of high－CSR acquirers, particularly when such practices are perceived as misaligned with shareholder value. Additional analyses, including 2SLS and GMM, further support these findings, demonstrating that CEO ownership curtails CSR activities. [Implications] This study contributes to the literature by providing a deeper understanding of the CSR spillover effect. Additionally, it examines the moderating role of CEO ownership, highlighting how managerial equity ownership influences strategic decisions in response to peer pressure