Depression will be one of the most serious illnesses in the 21(superscript st) century. It is one of the most commonly seen psychiatric disorders in adults and occurs more often in woman than in men. Empirical evidence shows that reproductive hormonal changes may impact on women's emotional state. Postpartum depression is one example of this emotional change. Most people in Taiwan regard physiological disease more importantly than psychological dysfunction. Therefore, postpartum depression has not received equal attention. However, mothers who suffer from postpartum depression significantly affect their child's development in language, cognition and attention. Suicides, and even infant homicide, are the most catastrophic results when this disorder is not properly identified and treated. This article discusses the etiology, diagnostic criteria, epidemiology, high-risk groups and treatment of postpartum depression by reviewing related literature, in order to enhance our understanding of this disease.