Birth of preterm infants is a stressful event for their parents, particularly for mothers. The mothers of preterm infants often feel hard to relate their infants because they have separated since their first days after delivery. Long term separation and less attractive, less responsive appearance of preterm infants also make it difficult to build mother-child relationships. In addition, the mothers of preterm infants are likely to have mood disorders such as depression, anxiety, and stress-related disorders. The mothers’ psychiatric illnesses affect the psychosocial development of preterm infants and are often regarded as a risk factor for child abuse and maltreatment in later life. Child abuse and maltreatment are also prevalent among preterm infants than the full term infants. Intervention from the early period of preterm birth is an important issue for both preterm infants and their mothers. Medical and co-medical professionals should pay attention to developmental outcome of preterm as well as psychosocial conditions of their mothers for the improvement of their mental health.