The purpose of this study was to investigate the effects of a one-day sheep-rearing experience on motivation and anxiety levels in patients with chronic mental illness. The study assessed changes in oxytocin and cortisol levels and brain activity in the prefrontal cortex, which is known to be associated with emotion and motivation. The study employed a non-randomized controlled trial design, with participants receiving both an intervention day (sheep rearing) and a control day (usual psychiatric day care) in a crossover fashion. Written informed consent was obtained from all participants. The intervention day consisted of hands-on sheep rearing activities, while the control day consisted of general activities available at the psychiatric day care center. Results showed that the sheep-raising experience had an equal effect on motivation and increased mean oxytocin levels. In addition, significantly more activity was observed in the dorsolateral prefrontal cortex (DLPFC) region of the brain compared to typical psychiatric daycare activities (p textless 0.032, p textless 0.043). Participants tended to have increased oxytocin levels after sheep rearing, and the activation of the DLPFC has not previously been observed in animal intervention studies. These are new findings in psychiatric occupational therapy that may have effects on social cognition and interpersonal relationships in patients with chronic mental illness.