Objective To evaluate the change and diagnosis value of D-dimer in acute ischemic stroke. Methods The serum levels of D-dimer in 78 normal controls and 78 patients with acute ischemic stroke were detected. Results The serum levels of D-dimer in patients with acute ischemic stroke were higher than that in normal controls (p<0.05). Compared with the normal controls, the serum levels of D-dimer in small infarction focus group, middling infarction focus group and large infarction focus group were obviously increased (p<0.05). The serum levels of D-dimer had good linear correlation with the area of infarction focus（r=0.926，p<0.05）. The serum levels of D-dimer in patients with acute ischemic stroke were obviously increased, and showed higher with the increasing of the area of infarction focus. Conclusion The serum levels of D-dimer has an important significance in the auxiliary diagnosis of acute ischemic stroke.