Objective: Xanthotoxin (XAT) is a linear furanocoumarin mainly extracted from the plants Ammi majus L. XAT has been reported the apoptosis of tumor cells, anti-convulsant, neuroprotective effect, antioxidative activity, and vasorelaxant effects. This study aimed to investigate the vascular protective effects and underlying molecular mechanisms of XAT. Methods: XAT’s activity was studied in rat thoracic aortas, isolated with aortic rings, and human umbilical vein endothelial cells (HUVECs). Results: XAT induced endothelium-dependent vasodilation in a concentration-dependent manner in the isolated rat thoracic aortas. Removal of endothelium or pretreatment of aortic rings with L-NAME, 1 H-[1,2,4]-oxadiazolo-[4,3- a]-quinoxalin-1-one, and wortmannin significantly inhibited XAT-induced relaxation. In addition, treatment with thapsigargin, 2-aminoethyl diphenylborinate, Gd<sup>3+</sup>, and 4-aminopyridine markedly attenuated the XAT-induced vasorelaxation. XAT increased nitric oxide production and Akt- endothelial NOS (eNOS) phosphorylation in HUVECs. Moreover, XAT attenuated the expression of TNF-α-induced cell adhesion molecules such as intercellular adhesion molecule, vascular cell adhesion molecule-1, and E-selectin. However, this effect was attenuated by the eNOS inhibitors L-NAME and asymmetric dimethylarginine. Conclusions: This study suggests that XAT induces vasorelaxation through the Akt-eNOS-cGMP pathway by activating the K<sub>V</sub> channel and inhibiting the L-type Ca<sup>2+</sup> channel. Furthermore, XAT exerts an inhibitory effect on vascular inflammation, which is correlated with the observed vascular protective effects.