Aim To explore the role of insulin resistance (IR)in atherosclerotic cerebral infarction (ACI)and lacunar cerebral infarction (LCI). Methods The serum concentrations of insulin after overnight fast and glucose load were determined by the use of radioimmunoassay and the serum concentrations of glucose, total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), lipoprotein (a) [Lp(a)], apolipoprotein A and B (ApoA, ApoB) after overnight fast and the serum concentrations of glucose after glucose load were measured by biochemical methods in 48 patients with ACI and 38 patients with LCI and 40 healthy control subjects. The plasmatic activities of tissue-type plasminogen activator (tPA)and plasminogen activator inhibitor-1 (PAI-1) were assayed by chromgenic substrate methods and levels of blood pressure and body mass index (BMI) was tested by routine ways in all subjects. Insulin sensitivity index (ISI) was estimated by the negative natural logarithm of the verse of fasting serum glucose and insulin product. Results The serum concentrations of glucose and insulin after overnight fast and glucose load (6.6±3.2 mmol/L and 6.3±2.3 mmol/L, 9.2±2.3 mmol/L and 9.2±2.5 mmol/L, 13.6±9.1 mIU/L and 13.4±8.0 mIU/L, 99.0±54.3 mIU/L and 98.4±53.9 mIU/L) were significantly higher in the two groups of cerebral infarction compared with the healthy control subjects (p<0.01), while the ISI (-4.20±0.24 and -4.19±1.02) in the two groups of cerebral infarction was significantly lower compared with the healthy control subjects (p<0.01). The increased levels of SBP(150.2±18.2 mmHg and 152.4±13.6 mmHg), DBP(96.2±12.7 mmHg and 97.4±18.6 mmHg), TG(1.71±0.68 mmol/L and 1.68±0.99 mmol/L), LDL(3.06±0.29 mmol/L and 3.01±0.40 mmol/L), TC(5.11±0.35 mmol/L and 4.98±0.34 mmol/L), Lp(a) (238±202 mg/L and 234±217 mg/L), PAI-1(880±350 AU/L and 870±150 AU/L) and BMI (26.5±1.1 kg/m2 and 26.3±2.0 kg/m2)were significantly observed in the two groups of cerebral infarction compared with the healthy control subjects (p<0.01), whereas decreased levels of HDL (1.24±0.48 mmol/L, 1.23±0.18 mmol/L)and tPA (0.28±0.16 kIU/L, 0.25±0.18 kIU/L) were detected significantly in the two groups of cerebral infarction compared with the healthy control subjects (p<0.01). The difference of all above parameters between two patients` groups had no statistical significance(p<0.05). In the patients with ACI and the patients with LCI, the ISI was negatively associated with the increased level of SBP, DBP, TG, ApoB, PAI-1 and BMI, but the ISI was positively associated with the decreased levels of HDL and ApoA, whereas the ISI was not associated with the levels of TC, LDL, Lp (a) and tPA. Conclusions IR which is the important risk factor in ACI and LCI plays an important part in both the atherosclerosis of large and medium cerebral arteries and the arteriosclerosis of small cerebral arteries.