Breastfeeding is the best source of nutrition for every infant, and exclusive breastfeeding for 6 months is usually optimal in the common clinical situation. However, inappropriate complementary feeding could lead to a nutrient-deficient status, such as iron deficiency anemia, vitamin D deficiency, and growth faltering. The recent epidemic outbreak of obesity in Korean children emphasizes the need for us to control children's daily sedentary life style and their intakes of high caloric foods in order to prevent obesity. Recent assessment of breastfeeding in Korea has shown that the rate is between 63% and 89%; thus, up-to-dated evidence-based nutritional management of breastfeeding infants to prevent common nutrient deficiencies or excesses should be taught to all clinicians and health care providers.