Emotion regulation (ER) is crucial for children’s mental health in general and traumatic stress in particular. Therefore, therapeutic interventions for posttraumatic stress symptoms (PTSS) address ER in various ways. We examined whether a psychosocial intervention (Teaching Recovery Techniques; TRT) could increase functional ER and decrease dysfunctional ER, and whether the positive ER change mediates the intervention effects on children’s mental health in a war context. Participants were 482 Palestinian children (girls 49.4%; 10-13 years, M = 11.29, SD = .68) who were randomized either to the TRT or the waiting-list control groups. They reported emotion regulation (ERQ; Rydell, Thorell, & Bohlin, 2007), PTS (CRIES-R), depressive (Birleson, Hudson, Gray-Buchanan, & Wolff, 1987), and psychological distress (SDQ) symptoms and psychosocial well-being at baseline (T1), postintervention at 3 months (T2), and the 9-month follow-up (T3). Results show that the TRT intervention was not effective in changing ER, but there was a general decrease in ER intensity. ER did not mediate the intervention effects on children’s mental health, but the decrease in the ER intensity was associated with better mental health, indicated by the decrease in posttraumatic, depressive, and distress symptoms and the increase in psychosocial well-being.