The present study aimed to examine how perfectionism is contributing to social anxiety and its cognitive processes of post-event rumination and self-perception of performance following a speech task. Forty-eight undergraduate students completed measures of perfectionism and trait social anxiety prior to performing a 3-min impromptu speech task. Immediately following the speech task, participants rated their state anxiety and self-perception of performance, and 24hr later, their level of post-event rumination was measured. Structural equation modelling revealed that perfectionism, in the form of socially prescribed perfectionism and doubts about actions, directly influences trait social anxiety, and indirectly influences post-event rumination and self-perception of performance through its relationship with trait social anxiety and state anxiety. This is the first study to investigate how perfectionism is contributing to social anxiety and its cognitive processes. The findings of this study provide evidence in support of the potential predictive role of perfectionism in social anxiety.