Previous studies indicated that oxytocin plays an important role in human trust, which is impaired in patients with severe mental disorders. In this study, we measured plasma oxytocin levels in patients with schizophrenia (n=50) and in healthy controls (n=50) after neutral and trust-related interpersonal interactions. Trust-related interactions were associated with increased oxytocin levels in controls. This effect was absent in patients with schizophrenia. Low oxytocin levels measured after trust-related interactions significantly predicted the negative symptoms of schizophrenia but were not related to positive symptoms, depression, anxiety, and neuropsychological functions. These results suggest that decreased trust-related oxytocin release is related to the negative symptoms and may be associated with social withdrawal, isolation, and flattened affect in schizophrenia.