The purpose of this study was to synthesize the effect size of Behavioral Activation (BA) on posttraumatic stress disorder (PTSD) symptoms and comorbid depressive symptoms, and to discuss the applicability of BA for PTSD. For this purpose, 13 studies published in international journals between 2006 and 2024 that met the inclusion criteria (4 randomized controlled trials and 9 non-randomized controlled trials) were analyzed, including a total of 725 trauma-exposed participants. A random-effects model meta-analysis using R revealed that the mean effect size of BA for PTSD symptoms was –.804 (95% CI: –.96 to –.54, p < .001). After trim-and-fill analysis, the effect size remained moderate at –.685 (95% CI: –.86 to –.51). For depressive symptoms, the effect size of BA was –.716 (95% CI: –.92 to –.52, p < .001), and remained moderate after trim-and-fill adjustment (–.521, 95% CI: –.73 to –.31). Moderator analyses were conducted for trauma type, study design (randomized vs. non-randomized), treatment type (BA alone vs. combined with other treatments), and comorbidity status (PTSD alone vs. PTSD with depression). However, no significant differences in effect size were found across these moderators. These findings support the efficacy of BA in reducing both PTSD and depressive symptoms, and the study concludes with a discussion of key clinical implications and directions for future research.