Appraisals and emotional regulation play a central role in posttraumatic stress disorder (PTSD). Despite research demonstrating cultural differences in everyday appraisals and emotion regulation, little research has investigated the influence of culture on these processes in PTSD. This study examined cultural differences in the associations between appraisals, emotion regulation and PTSD symptoms using trauma survivors from an individualistic Western culture (Australia) and a collectivistic Asian culture (Malaysia). Trauma survivors (N = 228; 107 Australian with European cultural heritage, 121 Malaysian with Malay, Indian or Chinese cultural heritage) completed an on-line survey assessing PTSD (PTSD Checklist for the DSM-5 with Life Events Checklist), appraisals (trauma-related, fatalism, cultural beliefs about adversity) and emotion regulation (suppression, reappraisal, interpersonal). The Malaysian group reported significantly greater fatalism, cultural beliefs about adversity, suppression and interpersonal emotion regulation than the Australian group. Greater trauma-specific appraisals, greater suppression, fewer cultural beliefs about adversity, and less use of social skills to enhance positivity were generally associated with greater PTSD symptom severity, with little evidence of cultural group moderating these associations. Interdependent self-construal mediated the relationships between cultural adversity beliefs, enhanced positivity, reappraisal, perspective taking and PTSD symptoms. Independent self-construal mediated the relationships between fatalism and perspective taking and PTSD symptoms. Cultural group did not moderate these indirect effects. Interdependent self-construal mediated the associations between interpersonal regulation strategies of soothing and social modelling with PTSD symptoms for the Malaysian but not the Australian group. These findings demonstrate the importance of considering self-construal and culture in understanding factors associated with PTSD.