This study examined the mediating role of the level of state self-compassion in the relationship between social anxiety level and negative post-event rumination. Fifty-five nonclinical undergraduate students first completed a self-report inventory of social anxiety. One week later, they made an impromptu speech in front of a video camera and a researcher. Following their speech, their levels of state self-compassion were measured, and then their levels of negative post-event rumination were assessed after a procedure to induce post-event rumination. The level of social anxiety was significantly correlated with both the levels of state self-compassion and negative post-event rumination. The level of state self-compassion was significantly correlated with the level of negative post-event rumination in the expected direction. Moreover, the level of state self-compassion fully mediated the relationship between social anxiety level and negative post-event rumination. The same results were also found when only participants with social anxiety were targeted. These results provide a theoretical basis to support the possibility that intervention to raise the level of state self-compassion will be effective in alleviating negative post-event rumination of individuals with social anxiety symptoms. Finally, implications and limitations of this study are discussed.