Background Coenzyme Q10 (CoQ10, ubiquinone) – endogenously synthesized highly mobile electron carrier in the mitochondrial respiratory chain - acts as an antioxidant and it can inhibit superoxide generation by endothelial cells. Coenzyme Q10 deficiency has been suggested to be involved in the impairment of endothelial dysfunction. Despite the fact of potent antioxidative properties of Coenzyme Q10 and its possible favorable effect on endothelial function, clinical studies are still rare. Therefore, We investigated the relationship between the levels of plasma coenzyme Q10 and endothelial function in hypercholesterolemia. Methods We measured plasma lipids, C-reactive protein, serum intracellular cell adhesion molecule (ICAM-1) and oxidized LDL using ELISA and plasma coenzyme Q10 levels (RP-HPLC) in nondiabetic patients with hypercholesterolemia (mean age 59 yrs, 25 males and 51 females, LDL-c>=130mg/dL). Results The results showed that significant negative correlation between serum ICAM-1 and coenzyme Q10 levels (r=-0.260, p<0.05) and positive correlation between serum ICAM-1 and oxidized LDL (r=0.298, p<0.01) were observed in total subjects. Plasma coenzyme Q10 was negatively correlated with triglyceride levels (r=-0.212, p<0.05) and oxidized LDL (r=-0.152, p=0.08). Stepwise multiple linear regression showed that increased plasma coenzyme Q10 levels was independently contributed to the decreased serum ICAM-1 (p<0.01). These effects remained statistically significant after adjusting age, gender, body mass index and traditional cardiovascular risks including blood lipids, C-reactive protein and oxidized LDL levels. Conclusion In summary, increased coenzyme Q10 levels are related to the decreased ICAM-1 levels, which favorably influences endothelial function. Further intervention study is needed to clarify the therapeutic effect of coenzyme Q10 on the endothelial function.