Objectives: ：This study aimed to investigate the mediating effect of post-traumatic stress symptoms on the relationship between affective temperaments and depression in psychiatric patients. Methods: ：A total of 200 psychiatric outpatients and inpatients completed TEMPS-A short version (Temperament Evaluation of the Memphis, Pisa, and San Diego Autoquestionnaire), the Korean-Beck Depression Inventory-II, and the PTSD Checklist for DSM-5. Data analysis was conducted using regression analyses and bootstrap sampling. Results: ：The results indicated that post-traumatic stress symptoms mediated the relationship between cyclothymic, depressive, and anxious temperaments with depression. Conclusions ：Cyclothymic, depressive, and anxious temperaments influence depression through post-trau-matic stress symptoms. This suggests the importance of considering subtypes of affective temperament and intervening in post-traumatic stress symptoms in order to prevent depression in psychiatric patients.