<p>Removing anonymity in social media may stimulate firm misconduct as it reduces social media’s monitoring effects. This paper employs China’s 2015 social media real-name registration policy as a quasi-natural experiment that requires internet users to register their real ID with the government. Results indicate that the policy caused a robust and economically meaningful increase in corporate greenwashing which is a classical misconduct. Results are robust with various robustness checks. Further analysis demonstrates that removing anonymity attenuates social media’s monitoring role in corporate greenwashing by mitigating three channels: reputation cost, market pressure from investors and regulation pressure that social media exerts on firms. Theoretically, our findings identify user anonymity as a key institutional condition enabling social media to function as an informal governance mechanism. The results also highlight a regulatory trade-off: identity-verification rules may curb online harm but can inadvertently weaken external oversight of firm misconduct.</p>