INTRODUCTION: Elevated fear of negative evaluation (FNE) and fear of positive evaluation (FPE) are thought to play key roles in the maintenance of social anxiety disorder (SAD). Although efficacious therapies exist for SAD, the potential mediating and moderating effects of FNE and FPE on social anxiety treatment outcome have not been examined. METHODS: This sample comprised a secondary analysis of 210 individuals who participated in one of three randomized controlled trials for the treatment of SAD. Participants were randomized to: individual cognitive behavioral therapy (CBT), group CBT, community mindfulness-based stress reduction (MBSR), group MBSR, or they were randomized to waitlist and offered treatment after waitlist. Assessments were completed pre- and post-treatment/waitlist and, for the treatment groups, at three-month follow-up. RESULTS: CBT and MBSR led to greater reductions in FNE and FPE than waitlist, with CBT more efficacious in reducing FPE than MBSR. For both CBT (vs. waitlist) and MBSR (vs. waitlist), there were significant indirect effects on post-treatment social anxiety through both FNE and FPE, and the indirect effect through FPE was greater for CBT than MBSR. However, in the fully longitudinal model testing mediation, CBT and MBSR were not differentially mediated by FPE. Baseline FNE and FPE each moderated CBT treatment outcome compared to waitlist - higher baseline FNE and FPE were associated with higher baseline social anxiety and greater reductions in social anxiety during CBT. DISCUSSION: FNE and FPE contributed in sometimes similar and sometimes distinct ways to the mediation and moderation of psychosocial approaches for treating SAD. This supports the importance of distinguishing between fears of negative and positive evaluation in the assessment and treatment of SAD.