Abstract: 108 geriatric patients with ischemic cerebrovascular diseases were treated with low dose aspirin（Acetylsalicylic acid, ASA）. Daily doses of 100 mg, 50 mg and 25 mg were administered respectively to three groups of 36 patients each. All the groups showed satisfactory results, with the best in the 50 mg group. Changes in platelet aggregation responses were dyna- mically observed in 64 cases. Monitoring of 22 normal subjects revealed that inhibition on platelet aggregation with a dose of 300 mg or 100 mg could last as long as 7 days. This suggests that, clinically, doses of 100 mg or less can be used effectively. Satisfactory inhibitive effects on platelet aggregation were observed in all the three groups with 14 patients each given dally doses of 100 mg, 50 mg and 25 mg in the four weeks of observation after ingestion of the drug, with the most desirable degree of inhibition achieved in the 50 mg group. Therefore, We recommend 50 mg/d as the optimal dosage for low dose aspirin therapy in geriatric iscbemic cerebrovascular patients.