Background: Being overweight is a common problem among chronic schizophrenic patients. However, these patients lack related exercise interventions that are both effective and convenient. Purpose: To explore the effects of a biosensing game intervention on the health-related fitness of chronic schizophrenic patients. Method: Two rehabilitation wards at a psychiatric hospital in New Taipei City were selected as the study sites. Simple random sampling was used to recruit participants. Participants in the experimental group received a 12-week biosensing game intervention, while participants in the control group received routine nursing care only. The study instruments included a demographic data sheet and anthropometric measurements. In addition, health-related fitness variables including cardiovascular endurance, muscular endurance, flexibility, and body composition (e.g., body mass index (BMI), waist-hip ratio, and body fat) were used as outcome indicators. Results: A total of 35 patients participated in the experimental group and 35 patients participated in the control group. The results showed that the mean differences between the pre-test and post-test values for body weight (t = 6.07, p ＜ .01), BMI (t = 5.79, p ＜ .01), and waist-hip ratio (t = 2.87, p ＜ .05) differed significantly, with the experimental group performing better than the control group on all three indicators. Conclusions / Implications for Practice: The results indicate that this 12-week intervention holds the potential to help chronic schizophrenic patients improve their health-related fitness, especially in terms of body weight, BMI, and waist-hip ratio. This study may be used as a reference for the promotion of health-related fitness programs in psychiatric institutes in the future.