Background: The present study aims to evaluate the in vitro vasorelaxant effect of Artemisia herba alba (Ah) aqueous extract.Method: Aortic rings were isolated from spontaneously hypertensive rats and incubated in aqueous Ah extract at the following doses: 3, 5, 10 and 20 mg/ml. Incubation of aqueous Ah extract for 30 minutes produced a significant shift of the dose response curve to Norepinephrine (NE) (10-8 to 10-5 M) (p<0.001). Results: Endothelium ablation significantly reduced the vasorelaxant effect of aqueous Ah extract (p<0.001). In addition, inhibition of vascular nitric oxide by Nω-Nitro-L-Arginine Methyl (LNAME) produced a significant reduction in the vasorelaxant effect of aqueous Ah extract (p<0.001). Conclusion: We conclude that aqueous Ah extract at a dose of 20 mg/ml possess an in vitro vasorelaxant effect which seems to be dependent on the endothelium vasorelaxant factors involving nitric oxide synthesis.