Background: Serum concentration of high density lipoprotein (HDL) more than 60mg/dL was known to have cardioprotective effect. Coronary vasospasm is a manifestation of endothelial dysfunction, can cause angina and acute coronary syndrome. We investigated whether high serum HDL have beneficial effect on coronary endothelial function as assessed by acetylcholine (Ach) provocation test. Methods: Among angina patients (pts) who underwent coronary angiography with Ach provocation test from January 2004 to august 2010, a total of 1300 patients were enrolled and retrospectively analyzed. Ach provocation test was performed by intracoronary infusion of Ach with incremental dosage (20, 50, 100µg). Vasoconstriction more than 70% by visual assessment was considered as positive provocation test. Angiographic parameters were compared between low HDL group (< 60mg/dL, n=994) and high HDL group (��� 60mg/dL, n=306) Results: Baseline characteristics were similar between the two groups except male gender (52.3% vs. 29.7%, P<0.01), smoking (23.9% vs. 17.0%, P=0.01), and aspirin use (6.6% vs. 3.6%, P=0.048) were higher in the low HDL group. High HDL group showed significantly lower incidence of (+) provocation test results, severe vasoconstriction (> 70%) on the QCA measurement and multivessel involvement as compared with low HDL group (Table). These statistical differences were continued to be significant after adjustment of baseline differences. Conclusions: According to our study, high serum HDL level (��� 60mg/dL) was associated with less incidence of (+) provocation test, less severe vasoconstriction and multivessel involvemenet. High HDL at baseline may play an important role in coronary artery vasoreactivity, may preserve coronary endothelial function and afford cardioprotection.