Although impairments in social skills, including empathic abilities, are common in post-traumatic stress disorder (PTSD), the ability to feel compassion—a pro-social behavior that is based on empathy and drives us to help others—has never been assessed among these patients. The first aim of this study was to examine whether patients with PTSD suffer from deficits in compassion and to examine the association between the clusters of PTSD symptoms and these deficits. Furthermore, given that intranasal oxytocin (OT) has been suggested to possibly modulate social behaviors, the second aim of this study was to investigate whether intranasal OT may enhance compassion in these patients. Using a randomized, double-blind, placebo-controlled crossover design, we administered 24 IU of OT and placebo at a one-week interval to 32 patients with PTSD and to 30 matched healthy control participants. The results indicate that patients with PTSD exhibit deficits in compassion and that the numbing cluster emerged as the key predictor of those deficits. Moreover, the results indicate that a single intranasal dose of OT enhances compassion toward women (but not towards men), both in patients with PTSD and in controls. These results offer support for recent suggestions that intranasal OT may potentially be an effective pharmacological intervention for patients with PTSD.