We examined self-esteem as a mediator of the relationship between mindfulness and social anxiety in a Chinese cultural context. Participants comprised 508 Chinese undergraduate students, who completed the Mindful Attention Awareness Scale, Rosenberg Self-Esteem Scale, and Interaction Anxiousness Scale. Results showed that social anxiety was negatively correlated with mindfulness and self-esteem, and that mindfulness was positively correlated with self-esteem. Mediation analysis revealed that self-esteem partially mediated the association between mindfulness and social anxiety. Thus, we suggest that mindfulness decreases social anxiety because high mindfulness fosters high self-esteem. Mindfulness practice, for example, meditation, can be used as a preventive therapy to help Chinese adults to reduce their social anxiety, and can also enhance the self-esteem of socially anxious Chinese adults.