Mental health research has increasingly moved beyond linear risk models that view adversity as having uniform effects on psychological outcomes, toward identifying protective factors that shape responses to stress. This study examined social support as one such factor in the relationship between perceived stress and PTSD among South African university students. Participants (
n
= 491) completed the Perceived Stress Scale, the PTSD Checklist for DSM-5, and the Multidimensional Scale of Perceived Social Support. Moderation analysis found no significant direct effect of social support on PTSD. However, overall support, support from significant others, friends, and family, each moderated the relationship between perceived stress and PTSD. Specifically, the association between perceived stress and PTSD was stronger at low levels of social support and weaker at high levels. These findings highlight the buffering role of perceived social support and suggest that interventions strengthening support from multiple sources may reduce the impact of stress on PTSD symptoms.