Background/Aims: Patients with K/DOQI stage 5 chronic kidney disease (CKD) have higher incidence of cardiovascular events due to the oxidative stress and endothelial dysfunction (ED). The aim of this study is to evaluate the effects of N-acetylcysteine (NAC), which might prevent cardiovascular events by improving oxidative stress on endothelial cells in patients with CKD. Methods: Thirty uremic patients (age 40 ± 12 years, 6 males) on hemodialysis (HD) were evaluated for ED by using high-resolution Doppler ultrasound of brachial artery before and after 6 weeks of oral NAC (2 × 600 mg) medication. Also, 13 healthy controls (35 ± 9 years, 5 males) were included in the study. Reactive hyperemia following 5 min forearm ischemia was accepted as endothelium-dependent vasodilatation (flow-mediated dilatation; FMD) and compared to endothelium-independent vasodilatation in response to sublingual glyceril trinitrate (GTN). Results: Patients on HD had lower ΔFMD (0.28 ± 0.17 vs. 0.41 ± 0.11, p < 0.05) and FMD% (7.5 ± 5.05 vs. 11.33 ± 2.95, p < 0.05) than the controls. Baseline ΔGTN and GTN% were similar in two groups. NAC treatment significantly increased the ΔFMD (0.41 ± 0.11, p < 0.001 vs. baseline) and FMD% (10.59 ± 3.22, p < 0.01 vs. baseline) of patients on HD, while it had no effect on ΔGTN and GTN%. Conclusion: These results suggest that NAC treatment could improve the ED by preventing the reduction of FMD in patients on HD.