Objective To investigate the relationship between cytochrome P 450 (CYP)2C19*2 / *3 gene polymorphism and antiplatelet effect of clopidogre in patients with ischemic stroke. Methods A total of 102 consecutive patients with acute ischemic stroke admitted to the Suzhou Integrated Traditional and Western Medicine Hospital from November 2012 to February 2014 were enrolled. The patients allergic to clopidogre,intolerant to clopidogrel,and recently using clopidogre were excluded. The patients were divided into a strong metabolic type group (n = 39),a moderate metabolic type group (n = 54),and a week metabolic type group (n = 9)according to the conditions of CYP2C19*2 and *3 locus mutation. The genotypes of the CYP2C19*2 and *3 were detected by the direct gene sequencing method in all patients. The maximum aggregation ratio (MAR)of platelet and platelet reactivity index (PRI)were detected beforeand 7 d after taking clopidogre 75 mg. Results (1)According to the CYP2C19*2 and CYP2C19*3, the genotyping was performed. The strong metabolic type group included *1 / *1 type 39 cases (38. 2%);the moderate metabolic type group included *l / *2 type 44 cases (43. 1%);*l / *3 54 cases, 10 (9. 8%);and the week metabolic type group included *2 / * type 27 cases (6. 9%);*2 / *3 type 2 cases (2. 0%). No *3 / *3 type was detected. (2)There were no significant differences in MAR before taking clopidogrel among the 3 groups (all P > 0. 05). After taking clopidogrel for 7 days,MAR and PRI were detected from strong to weak,followed by the week metabolic type group (49 ± 12% vs. 64 ± 15%), the moderate metabolic type group (42 ± 13% vs. 56 ± 14%),and the strong metabolic type group (33 ± 10% vs. 43 ± 12%);MAR was detected from high to low,followed by the strong metabolic type group (20 ± 12%),the moderate metabolic type group (10 ± 8%),and the week metabolic type group (7 ± 3%). Comparing the moderate metabolic type group and the week metabolic type group with the strong metabolic type group,there were significant differences between MAR,the decreased MAR and PRI (all P < 0. 01). Comparing the week metabolic type group with the moderate metabolic type group,there were no significant differences between MAR,the decreased MAR and PRI (all P > 0. 05). Conclusion The CYP2C19*2 and *3 gene polymorphisms may affect MAR and PRI after taking clopidogrel in patients with ischemic stroke.