Objective: To explore the effects of Tai Chi on body mass index (BMI), exercise capacity, and mental health of overweight/obese adults, and investigate factors influencing adherence to enhance adherence of Tai Chi as a sustainable exercise method. Methods: A randomized, controlled, exploratory clinical trial was conducted paired with a qualitative study of adherence management. A total of 20 overweight/obese participants were randomly assigned to a standard Tai Chi group (experimental) and a simplified Tai Chi group (control) for an 8-week intervention, 10 patients in each group, with a 12-month follow-up. BMI was calculated and exercise capacity including an isokinetic muscle strength and balance ability test were evaluated. Mental health was assessed using the General Well-Being Schedule (GWB), Pittsburgh Sleep Quality Index (PSQI), and Coping Self Efficacy Scale (CSES) at baseline, 4th week, and 8th week, respectively. The qualitative research included open-interviews with Tai Chi practitioners and semi-structured interviews with subjects. Results: The intervention was conducted in Haidian Park, Beijing, China from October 6, 2022, to January 1, 2023, without dropouts. After an 8-week intervention, the participants in the experimental group exhibited a significant decrease in BMI (P<0.05). Both groups demonstrated significant improvements in exercise capacity (P<0.05). The experimental group exhibited a significant enhancement in the GWB, PSQI and CSES (P<0.05). Only GWB had significant difference in the control group (P<0.05). The experimental group surpassed the control group in GWB and CSES (P<0.05). The adherence rate was 87.5% in the experimental group and 57.9% in the control group after 8 weeks intervention. Analysis on adherence identified 15 themes, the top 3 themes mentioned were as follows: mind-body effects, online and on-site guidance, training schedule (for subjects); mind-body effects, difficulties in practicing, and understanding of Tai Chi (for practitioners). Conclusions: Both interventions were effective in improving exercise capacity. Tai Chi, integrating both physical and mental conditioning, reduced weight, improved exercise capacity and mental happiness, and increased adherence, providing a sustainable exercise program (ChiCTR2200063599). [ABSTRACT FROM AUTHOR]