This study investigated whether negative interpretations of ambiguous social information and fear of negative evaluation (FNE) mediate the relationship between intolerance of uncertainty (IU) and social anxiety subtypes, specifically social interaction anxiety and performance anxiety. Sixty-six participants completed measures examining IU, social interaction anxiety, social performance anxiety, fear of negative evaluation, and negative interpretation bias in the context of ambiguous social scenarios. As expected, fear of negative evaluation mediated the association between IU and social interaction anxiety, and the relationship between IU and performance anxiety. Negative interpretation bias, as measured by a higher likelihood of having negative interpretations of ambiguous social content come to mind, mediated the association between IU and both social anxiety subtypes; however, participants' belief in those negative interpretations did not. Results of this study suggest that difficulty tolerating uncertainty about perceived negative evaluation and about the meaning and possible consequences of ambiguous social situations may be a critical element in the development, maintenance, and/or exacerbation of social anxiety. Future studies should incorporate longitudinal designs using serial moderation models to examine the complex causal relations between IU, FNE, negative appraisals of ambiguous social content, and social anxiety subtypes.