While corporate social responsibility (CSR) has played an increasingly important role in corporate decision‐making, the role of CSR disclosure in a firm's investment activities remains poorly understood. This study investigates the impact of CSR disclosure on mergers and acquisitions (M&As), which are pivotal investment activities. We find that firms disclosing voluntary CSR reports experience significantly stronger market reactions to M&A announcements than those that do not disclose such reports. Specifically, acquisitions by voluntary CSR disclosers achieve 1.2% higher returns upon acquisition announcements, leading to a substantial increase in shareholder value. Our findings are consistent across a series of robustness tests. Additional analyses suggest that the positive market reactions are especially tied to voluntary disclosures concerning the protection of employees and customers, and that the quality and financial materiality of voluntary CSR disclosures amplify positive market responses. We also find that voluntary CSR disclosers exhibit better long‐term post‐acquisition market and operational performance. Collectively, our findings suggest that voluntary CSR disclosures bolster acquisition returns by mitigating stakeholder resistance. Additionally, by leveraging the unique conditional CSR disclosure regulation in China and using a staggered DID design, we observe a diminished market reaction for acquirers following mandatory CSR disclosures. Overall, this research provides new insights into the contrasting effects of voluntary and mandatory CSR disclosures, emphasizing the vital role of effective stakeholder CSR communication in the success of M&As.