Social anxiety disorder (SAD) is defined as a marked and persistent fear of social situations in which an individual is exposed to potential scrutiny from others (American Psychiatric Association, 2013). Prominent models of SAD (Clark & Wells, 1995; Rapee & Heimberg, 1997) postulate that postevent processing (PEP), which involves reviewing a past social event in detail (typically in a negative way), serves as a key maintenance factor of SAD. The current study examined the efficacy of a single session cognitive restructuring or mindfulness strategy on decreasing PEP and its associated effects, and also investigated the cognitive processes involved. Seventy-four socially anxious participants completed a speech task to elicit PEP, were taught a cognitive restructuring, mindfulness, or control strategy to manage their negative thoughts related to the speech, and completed several questionnaires. Participants in the cognitive restructuring condition reported decreased PEP (degree and associated distress) and improved affect (but not reduced state anxiety), as compared to the control condition. Participants in the mindfulness condition also reported decreased PEP (degree but not associated distress) and improved affect (including reduced state anxiety), as compared to the control condition. No significant differences were found between the cognitive restructuring and mindfulness conditions. Participants in the cognitive restructuring condition also reported decreased beliefs about the perceived costs of negative social situations. Regardless of study condition, decreases in cost biases and maladaptive beliefs significantly predicted reductions in PEP. Thus, cognitive restructuring and mindfulness appear to be promising strategies to decrease PEP and its associated negative effects.