Abstract: Posttraumatic stress disorder (PTSD) is a debilitating condition that disproportionately impacts service members (SMs). Interoception interventions that target malleable, transdiagnostic risk factors for PTSD, such as the acceptance of uncomfortable internal sensations, may serve as potential options for military providers. The current study evaluated the efficacy of Reconnecting to Internal Sensations and Experiences (RISE)-an empirically supported interoception training focused on accepting and managing internal sensations-in reducing PTSD symptom severity. Active-duty SMs and veterans (N = 100) with probable PTSD were randomized to receive RISE or Healthy Habits (active control). Participants completed four weekly 30-min training modules, as well as survey assessments (PTSD symptom severity, not worrying/acceptance of uncomfortable internal sensations) at baseline, posttreatment, and 1-month follow-up. Mediation analysis evidenced a significant direct effect of RISE on improvements in not worrying/acceptance at posttreatment, B = 0.51, and not worrying/acceptance on reductions in PTSD symptom severity at follow-up, B = -3.76. Despite no direct effect of condition on PTSD symptoms, B = 2.66, a significant indirect effect was observed through improvements in not worrying/acceptance, B = -1.91, such that RISE led to increased not worrying/acceptance, which, in turn, was associated with decreases in PTSD symptom severity. These findings support acceptance of internal sensations as a key mechanism of change for improving PTSD. Further, the results provide preliminary evidence for RISE as a viable PTSD treatment supplement for SMs and provide preliminary support for the use of transdiagnostic tools developed with considerations for military cultural stigma and logistical concerns.