Background: Admission hyperglycemia is a predictor of poor prognosis after ischemic stroke (IS). Previous studies have found that admission hyperglycemia was related to clopidogrel high on-treatment platelet reactivity (HTPR) in diabetic patients with myocardial infarction. However, reports on associations between admission hyperglycemia and clopidogrel HTPR remain scarce in IS patients. In this study, we assessed the correlation between admission hyperglycemia and clopidogrel HTPR in patients with IS. Methods: In this retrospective study, we included IS patients who were treated with clopidogrel for at least 5 days. Thromboelastography (TEG) was used to evaluate the platelet function. Clopidogrel HTPR was defined if adenosine diphosphate (ADP)-induced platelet fibrin clot strength (MAADP)> 47 mm. Otherwise, it would be defined as clopidogrel normal on-treatment platelet reactivity (NTPR). Two groups were divided according to admission glucose of 7.8 mmol/L, consistent with previous studies on admission hyperglycemia. The independent risk factors of clopidogrel HTPR were assessed by multivariate logistic regression analysis.Results: A total of 147 patients were evaluated, and 42(28.57%) of patients were identified as clopidogrel HTPR. In the hyperglycemia group (admission glucose level >= 7.8mmol/L), 40.38% patients were defined as clopidogrel HTPR, which was significantly higher than in the normoglycemia group (22.11%, admission glucose level<7.8mmol/L) (P=0.019). According to multivariate analysis, hyperglycemia was independently associated with clopidogrel HTPR (OR=8.36, 1.47-47.55, P=0.017). Admission glucose level was linearly correlated with MAADP (r=0.29, P=0.005). Furthermore, with the increase of admission glucose level tertiles, the incidence of clopidogrel HTPR increased gradually (P for trend=0.008). Conclusions: Admission hyperglycemia is an independent predictor of clopidogrel HTPR and the glucose level is linearly correlated with MAADP in IS patients. Besides, with the increase of glucose level tertiles, the incidence of clopidogrel HTPR increases gradually.