Abstract: Objectives: This secondary analysis examined five facets of mindful awareness as potential moderators of clinical outcomes using data from a randomized controlled trial (RCT) that compared Mantram Repetition Program (MRP) with present-centered therapy (PCT) in veterans with post-traumatic stress disorder (PTSD). Methods: Data were examined from 173 veterans with military-related PTSD randomly assigned to receive eight sessions of MRP (n = 89) or PCT (n = 84). Clinician-administered and self-report measures of mindfulness (Five Facet Mindfulness Questionnaire [FFMQ]), PTSD severity, insomnia symptoms, and depression symptoms, and were obtained pre- and post-intervention. Hierarchical regressions were used to test for FFMQ moderation on clinical outcomes within the two treatment groups. Results: For those with greater ability to “describe their internal experience” (+1 standard deviation [SD]), MRP was associated with lower PTSD hyperarousal symptoms post-intervention than PCT (p < 0.001). For those with lower “nonreactivity to internal stimuli” (-1 SD), MRP was associated with greater reductions in PTSD avoidance and numbing symptoms and insomnia compared with PCT (all ps < 0.002). Conclusions: Pre-intervention mindfulness domains of “describe” and “nonreactivity to inner experience” differentially predicted improvements in PTSD and insomnia symptoms for MRP as compared with PCT subjects. The FFMQ may be an important tool for predicting patient preparedness for mindfulness-based interventions, such as MRP.