Cognitive models of social anxiety predict that interpretation bias mediates the relationship between level of social anxiety and state anxiety in response to social-evaluative threat. We tested this prediction in 67 socially anxious undergraduates. Participants completed self-report measures of social anxiety and interpretation bias, and two days later they completed an impromptu speech. Mediational analyses supported the hypothesis that interpretation bias mediates the effect of social anxiety on state anxiety in response to the speech. This relationship was specific to negative interpretation of ambiguous social scenarios. The current findings support cognitive models of social phobia and add to the empirical base supporting the role of interpretation bias in social anxiety.