PTSD patients show alterations of the immune system, mainly a ‘low-grade inflammation’. Psychotherapeutic treatments are meant to reduce symptom burden of PTSD patients but 30–50% of PTSD patients do not benefit from psychotherapy. Therefore, in this study, the predictive effect of cytokine levels on therapy outcome are investigated. Pro- (IL-6) and anti-inflammatory (IL-10) cytokines in female PTSD patients (N = 17) were assessed under acute stress during a Trier social stress test (TSST) before therapeutic treatment. The predictive effects of IL-6 and IL-10 on therapy outcome (SCL_GSI, BDI) after an inpatient psychotherapeutic treatment at the University Medical Center Carl Gustav Carus, Technische Universität Dresden was investigated. Areas under the curve with respect to ground (AUCG) and increase (AUCI) for IL-6 and IL-10 levels during the TSST were calculated and used as predictors in regression analyses with pre-treatment scores. Models including all three predictors show good model fits (R2 = 0.255 to 0.744). Models including AUCG and AUCI scores show superior fits compared with models including pre-treatment scores alone (ΔR2 = 0.196 to 0.444). IL-6 AUCG and AUCI scores are significant predictors for post-treatment SCL-GSI and BDI (β = −0.554 to 0.853), whereas IL-10 AUCG significantly predicts SCL-GSI and BDI (β = −0.449 to −0.509). Therefore, pro- and anti-inflammatory IL-6 and IL-10 levels under acute stress before therapy predict therapy outcome of female PTSD patients regarding general symptom burden and depressive symptoms. Future studies should further address the link between inflammation and therapy outcome, especially underlying mechanisms and influencing factors.