Previous studies suggested that Tai Chi may be beneficial for T2DM patients. However, no studies have investigated the effectiveness of Tai Chi for comorbid depression in T2DM patients, as well as the optimal frequency of Tai Chi. Thus, we intend to investigate the effectiveness of Tai Chi for comorbid depression in T2DM patients and test whether the effectiveness of Tai Chi depends on its frequency.

Inclusion Criteria:

• Participants diagnosed with depression by experienced psychiatrist;
• Participants diagnosed with T2DM by experienced endocrinologist;
• Participants aged between 18~75 years;
• Participants with HbA1c ranges from 6.5% to 8.5%;
• Participants with Hamilton Depression Scale (HAMD) (24-item-version) ranges from 20~35 scores;
• Participants passed the Physical Activity Readiness Questionnaire (PAR-Q);
• Participants willing to complete 12-week intervention and 12-week follow-up.
• Participants willing to sign informed consent form.

Exclusion Criteria:

• Participants with uncontrolled hypertension (SBP >160mmHg or DBP >100mmHg after taking hypotensive drugs);
• Participants with severe diabetic complications;
• Regular exercisers (at least 20 minutes/time, 3 times/week) in the last 3 months;
• Participants with cognitive impairment (Montreal Cognitive Assessment [MoCA] scores <26);
• Participants with history of bipolar disorder or schizophrenia or other mental illness;
• Participants with contraindications to exercise;
• Participants with acute, infectious diseases, cancer, or serious neurological disease, cardiovascular disease, pulmonary disease or other serious medical conditions limiting the ability;
• Participants taking psychoactive drugs;
• Participants participating in other clinical trials at the same time.