<p>The impact of real name versus anonymity on social media represents a contentious issue. This study leverages a natural experiment in China and uses social media data from financial markets to investigate the impact of mandatory real-name identification on the informativeness of social media. We find a decrease in the informativeness of social media after the mandatory real-name identification. At the user level, our tests show that mandatory real-name identification primarily diminishes the informativeness of postings generated by high-follower users, who wield considerable influence in the capital market. Moreover, after the mandatory real-name identification, the percentage of postings with valuable information decreased and the language style became more ambiguous and lacked opinions. These findings align with the idea that the consequences of mandatory real-name identification predominantly arise from an increased perception of regulatory risk among users. Overall, this study contributes significantly to the comprehension of how anonymity influences the informativeness of social media.</p>