Background <p>Research supports the relation between posttraumatic cognitions and symptoms of posttraumatic stress disorder (PTSD). Mindfulness and emotional dysregulation have theoretical and empirical links to both posttraumatic cognitions and PTSD symptoms, and may moderate the association between them. Thus, evaluating mindfulness and emotional dysregulation as moderators may inform strategies for buffering the impact of negative posttraumatic cognitions on PTSD symptoms.</p> Methods <p>We conducted an online cross-sectional study with a sample of 274 trauma-exposed undergraduate students with clinically elevated PTSD symptoms. Participants completed the PTSD checklist for <i>DSM-5</i>, posttraumatic cognitions inventory, five facet mindfulness questionnaire, and difficulties in emotion regulation scale.</p> Results <p>Multiple regression analyses utilizing a model-building approach revealed that the mindfulness facet of nonjudging moderated the relation between posttraumatic cognitions and PTSD symptoms. An exploratory analysis demonstrated that nonjudging specifically moderated the association of PTSD symptoms with negative cognitions about the world. In both cases, greater nonjudging weakened the relation between negative cognition and PTSD symptoms. A sensitivity analysis adjusting for sex indicated possible sex differences such that greater nonjudging buffered the association between posttraumatic cognitions and PTSD symptoms in females but not males.</p> Conclusions <p>Findings imply that future research should leverage nonjudging as a potential strategy for mitigating the impact of negative cognitions on PTSD symptoms, particularly among females.</p>