<p>The engagement of rumor posts on social media is influenced by a wide range of factors related to the spreader, yet the underlying mechanisms remain unclear. This study investigates how the personality traits of rumor spreaders on social media affect the engagement of their posts, with particular attention given to the mediating role of emotional expression. This study collects data from Weibo, a leading social media platform in China. Instead of relying on self-report measures, it infers users’ Big Five personality traits and emotional expressions from their 382,783 historical posts on Weibo, via a computational approach based on natural language processing. The dataset includes rumor posts and prior social media activity from 545 identified rumor spreaders. The results indicate that among the Big Five traits, openness is negatively associated with the engagement of rumor posts, whereas agreeableness is positively associated with engagement. However, emotional expression in rumor posts partially mediates and weakens these effects. These findings contribute to our understanding of the relationship between personality traits and rumor dissemination and offer insights for identifying potential rumor spreaders from a personality perspective.</p>