As the most common nutrition deficiency, iron deficiency not only causes anemia but also influences the central nervous system development. Its pathogenesis is supposed to be the alteration of neurometabolism and neurotransmission in major brain structures, and the disruption of myelination. The first two years after birth is a crucial period for cognitive, behavior, and emotional development with fast brain growth. If iron deficiency occurs in this period, cognitive and psychomotor function cannot be restored in spite of adequate iron supplementation. Thus, iron deficiency in infancy should be considered as a serious disease.