Background: Sleep disturbance is common within days to weeks following a traumatic event and has been associated with emotion dysregulation, a strong risk factor for PTSD development. This study aims to examine if emotion dysregulation mediates the relationship between early post-trauma sleep disturbance and subsequent PTSD symptom severity. Methods: Adult participants ( n = 125) completed questionnaires regarding sleep disturbance (via Pittsburgh Sleep Quality Index Addendum; PSQI-A) and emotion dysregulation (via Difficulties in Emotion Regulation Scale; DERS) within 2 weeks after exposure to traumatic events. Results: PTSD symptom severity was assessed with PTSD Checklist for DSM-5 (PCL-5) at 3-month follow-up. There were strong correlations between PSQI-A, DERS, and PCL-5 (r ranges between .38 and .45). Mediation analysis further revealed significant indirect effects of overall emotion regulation difficulties in the relationship between sleep disturbance at 2 weeks and PTSD symptom severity at 3 months ( B = .372, SE = .136, 95% CI: [.128, .655]). Importantly, limited access to emotion regulation strategies emerged as the single, significant indirect effect in this relationship ( B = .465, SE = .204, 95% CI [.127, .910]) while modelling DERS subscales as multiple parallel mediators. Conclusions: Early post-trauma sleep disturbance is associated with PTSD symptoms over months, and acute emotion dysregulation explains part of this association. Those with limited emotion regulation strategies are at particular risk of developing PTSD symptoms. Early interventions focusing on the appropriate strategies for emotion regulation may be crucial for trauma-exposed individuals.