It has been suggested that reward processing and related neural substrates are disrupted in some common mental disorders such as depression, addiction, and anxiety. An increasing number of psychiatric studies have been applying reinforcement learning (RL) models to examine these disruptions in self-regarding learning (learning about rewards delivered to the learners themselves). A review of RL alterations associated with mental disorders in extant studies will be beneficial for uncovering the mechanisms of these health problems. Although impaired social reward processing is common in some mental disorders [e.g., post-traumatic stress disorder (PTSD), social anxiety and autism], RL has not been widely used to detect the potentially disrupted social reward learning, especially for other-regarding learning (learning about rewards delivered to others). Meanwhile, it has not been clear whether some drugs, e.g., oxytocin (OT), can alter other-regarding learning, so they may serve as a therapeutic intervention when related deficits occur. In the present set of studies, we summarized common and distinct features in terms of self-regarding RL disturbances among depression, addiction and anxiety disorders based on previous findings (Paper I), tested whether behavioral and neural self- and other-regarding RL were impaired in PTSD with and without comorbid depression (Paper II), and investigated OT's behavioral and neural effects on self- and other-regarding RL in healthy males (Paper III). The results of our literature review showed that the commonalities in all three mental disorders were inflexibility and inconsistent choices, and the differences included decreased learning rates in depression, a higher weight to rewards versus punishments in addiction, and hypersensitivity to punishments in anxiety. The results of the PTSD study demonstrated impaired behavioral other-regarding learning in PTSD patients with and without depression, supposedly due to their hypervigilance to unexpected outcomes for others, as evidenced by the heightened responses in their inferior parietal lobule. The OT study detected OT's effects of attenuating behavioral other-regarding learning, as well as the neural coding of unexpected outcomes for others in the anterior cingulate cortex. These findings provide new evidence of self- and other-regarding RL alterations in mental disorders, reveal potential targets for their treatments, and bring caution for using OT as a therapeutic intervention. / Doctor of Philosophy / People learn to make choices to gain rewards and to avoid punishments delivered to themselves. As social animals, people also take account of outcomes delivered to others when learning. With the help of computational modeling, previous studies have found abnormal reward learning for oneself in people with mental health problems. To better understand mental illnesses, we summarized the similarities and differences of the learning abnormalities reported in previous studies about depression, addiction, and anxiety. We have found that people with these mental illnesses all tend to be inflexible and make more random choices when learning. As for the differences, people with depression tend to learn slower; people with addiction tend to see gaining rewards as more important than avoiding punishments; and people with anxiety tend to be oversensitive to punishments. Using computational modeling and imaging of brain function, we also tested whether learning for other was abnormal in post-traumatic stress disorder (PTSD), and found that, compared to healthy people, PTSD patients had slower learning for others' rewards, and the inferior parietal lobule, a brain region for processing social information, showed higher responses to unexpected outcomes for others. In another study, we examined whether oxytocin (OT), a neuropeptide that has been reported to change people's social functions, could influence reward learning for others in healthy males. The results showed that OT slowed down people's learning for others, and also decreased the neural learning signals in the anterior cingulate cortex, a region involved in processing other's outcomes. Our findings provide new information about how reward learning for oneself and others are changed in mental illnesses, reveal potential targets for their treatments, and bring caution for using OT as a therapeutic intervention.