Objective To evaluate the influence of hyperglycemia in elderly diabetic patients with acute cerebral infarction. Methods We retrospectively analyzed 126 acute cerebral infarction cases among 232 elderly diabetic patients who had been treated in Manzhouli Southern District Hospital of Inner Mongolia from Jan, 2010 to Dec, 2011. All the patients were divided into three groups by the level of fasting plasma glucose (FPG) acquired when they were admitted to hospital : group A (FPG 7.0-11.1mmol/L), group B(FPG 11.1-16.7mmol/L), and group C (FPG ≥16.7mmol/L) . Meanwhile, the severity of cerebral infarction was categorized as mild, moderate and severe. The relationship among level of hyperglycemia, severity of disease, the size of brain CT scan and acute prognosis were evaluated. Results No statistically significant difference was found in size of infarction, the numbers of patients with different degree of neural function defect, and the numbers of patients with diverse prognosis (P＞0.05). Compared with group A and group B, the infarct size was statistically significantly larger in group C (P＜0.05), patients in which had blood glucose over 16.7mmol/L. Compared with group A, less patients in group C had mild and moderate neurological impairment, and more patient had severe impairment( P＜0.01). Less patients in group C had good prognosis ( roughly cure or apparently improved, P＜0.01), and more patients had bad prognosis( death, getting worse or no change, P＜0.01) than patients in group A. Conclusion In patients with diabetes and cerebral stroke, the severity of clinical symptoms and prognosis are closely related to the level of blood glucose. Level of blood glucose over 16.7mmol/L was an important indicator of bad prognosis in acute period.