This randomized double-blind controlled study was carried out to investigate the effect of 100 mg acetylsalicylic acid (ASA) per day on the secondary prevention of ischemic stroke. Patients who suffered a first ischemic stroke from 13 participating hospitals were enrolled. They were independent or only partially dependent in activities of daily living and all had received brain CT for diagnosis. Eligible patients were randomly allocated to the 100 mg ASA or the nicametate citrate (a vasodilator) groups, and trial medications were started within three to six weeks after the onset of stroke. The primary end point was cerebral reinfarction, and intracranial hemorrhage was classified as an adverse event. Four hundred and sixty-six patients participated in this study; and 222 cases (136 males and 86 females) were allocated to the ASA group while 244 cases (150 males and 94 females) were assigned to the nicametate group. No significant difference in baseline characteristics between the two groups was observed. Cerebral reinfarction developed 6.3% (14/222) in the ASA group and 11.9% (29/244) in the nicametate group. According to the Cox's proportional hazards model, the estimated risk ratio (ASA group vs. nicametate group) was 0.538, with a 95% confidence interval of 0.284-1.019. The result was of borderline statistical significance. The risk for cerebral reinfarction was reduced by almost 50% among those who took 100 mg ASA versus those who took nicametate.