By transcranial Doppler (TCD) and electroencephalogram (EEG), twenty patients with hyperthyroidism were studied. The abnormal rate of TCD and EEG was 95% and 70% respectively. The result revealed that cerebral function abnormality and cerebrovascular hemodynamics abnormality may happen at the same time in the hyperthyroidism. The paper indicated that although TCD and EEG are no specificity for clinical diagnosis, both may provid objective index for diagnosis, treatment and prognosis of this disease.