A 56-year-old woman presented with severe iron-deficiency anemia and memory disturbance. She had been in a state of severe iron deficiency for many years due to an unbalanced diet. Aerobic exercise test revealed an abnormal elevation of lactate and pyruvate reflecting mitochondrial dysfunction. After iron replacement therapy, WAIS verbal IQ score improved from 63 to 83, and levels of lactate and pyruvate on aerobic exercise test were normalized. We raise the possibility that severe and long-term iron deficiency anemia may cause memory disturbance due to mitochondrial dysfunction.