Abstract: Objective To investigate the clinical significance of serum homocysteine in patients with moyamoya disease. Methods 250 cases of serum samples of patients with moyamoya disease were collected from the department of neurosurgery. According to the MRA images the patients were divided into 6 phase groups, phase I, II and III were early stage in the development of moyamoya disease. Phase IV, V and VI were late stage in the development of moyamoya disease. The serum homocysteine levels in patients and 250 cases of normal control were detected. Results The serum homocysteine levels in patients with moyamoya disease were significantly higher than that of in normal controls (P<0.001). There were no significantly difference between late stage phase group with early stage group patients with moyamoya disease (P>0.05). Conclusion The serum homocysteine may play a role in blood vessel damage of moyamoya disease.