Abstract: Nitric Oxide (NO) donors such as L-arginine are a candidate to restores endothelial function. NO itself may change endothelial permeability which is an important factor to control vascular homeostasis. So, the effect of L-arginine on aorta and coronary arteries permeability was the objective of this study. 20 male rats were randomly divided into two groups of oral administrated L-arginine (4 g/l) and control. After five weeks of experiment, the serum level of nitrite by Griess reagent method and direct blood pressure were measured. The aorta and coronary arteries permeability were determined by extravasation of injected Evan Blue dye. The results indicate that after the 5 weeks of experiment, L-arginine increases mean arterial pressure (group I: 157±6, group II: 108.2±10.1 mmHg; p<0.05) and the serum level of nitrite(group I: 35.69±6.88, group II: 23.21±2.72 µmol/l; p<0.05) significantly. No statistical differences were observed in endothelial permeability of aorta (group I: 66.6±5.4, group II: 85.23±10.64 µg/g.tissue) and coronary arteries (group I: 28.2±3.17, group II: 22.83±1.39 µg/g. tissue) between the groups. Low dose L-arginine may increases the level of nitrite; last metabolite of NO in plasma, but its effect on aorta and coronary arteries permeability is not certain.