This study investigated the relationships between Type D personality, depression, and social support among ethnic Chinese coronary artery disease (CAD) patients undergoing percutaneous coronary interventions. Type D personality is associated with CAD, and may increase patients’ depression and mortality rate. However, very few studies have explored the relationships between depression and social support among ethnic Chinese Type D CAD patients. A longitudinal, repeated-measures design was used; 105 Taiwanese CAD patients undergoing a percutaneous coronary intervention were recruited between January and December 2015. A demographic questionnaire, Type D Scale, ENRICHD Social Support Inventory, and Patient Health Questionnaire-9 were completed by 102 participants (mean age = 64.42, SD = 13.67 years) at hospitalization, and at the second week and third month after discharge. Data were analyzed using t tests and a generalized estimating equation. Results indicated that 46.7% of participants who had Type D personality had lower social support and higher depression than did the remaining (non-Type D) participants. At two weeks after discharge, the improvement in social support was higher among Type D patients than non-Type D participants; the same was true for depression at two weeks and three months after discharge each. Type D Taiwanese CAD patients showed lower perceived social support and higher depression during hospitalization than did non-Type D participants. Furthermore, the more social support patients received at home, the lower was their depression. Health-care providers should provide continuous mental health care, conduct early screening of mental health issues, and ensure that patients receive sufficient social support to reduce depression.