OBJECTIVE： To investigate the vasodilatory effect mechanism of psoralen and bakuchiol. METHODS： The rat thoracic aorta was isolated to prepare vascular rings and de-endothelium vascular rings. Using contraction rate as index， the intact endothelium or de-endothelium vascular rings were pre-incubated with N-nitro-L-arginine methyl ester （L-NAME， 100 μmol/L）； vasodilatory effect of low-dose， medium-dose and high-dose of psoralen or bakuchiol（0.1，1，10 μmol/L）on aortic vessels pre- contracted with norepinephrine （NE， 1 μmol/L） or potassium chloride （KCl， 60 mmol/L） were investigated. The de-endothelium vascular rings were pre-incubated with calcium dependent potassium channel inhibitors tetraethylammonium chloride （TEA， 0.1 mmol/L） and inward rectifying potassium channel inhibitor barium chloride （BaCl2，0.1 mmol/L）； vasodilatory effect of low-dose， medium-dose and high-dose of bakuchiol （0.1， 1， 10 μmol/L） on de-endothelium vascular vessels pre-contracted with NE （1 μmol/L） were investigated. The microvascular endothelial cells were isolated by collagenase-neutral protease digestion； the effects of low-dose， medium-dose and high-dose of psoralen or bakuchiol （0.1， 1， 10 μmol/L） on the expression of eNOS protein were studied by ELISA. RESULTS： Psoralen and bakuchiol could significantly reduce the contraction rate of endothelium-intact aortic rings pre-contracted with NE（P＜0.01）； medium-dose and high-dose of psoralen and bakuchiol could significantly reduce the contraction rate of  endothelium-intact aortic rings pre-contracted with KCl（P＜0.05 or P＜0.01）； while the contraction rate could be increased by de-endothelium and NOS inhibition significantly （P＜0.05 or P＜0.01）. The medium-dose and high-dose of bakuchiol could significantly reduce the contraction rate of  de-endothelium vascular vessels pre-contracted with NE （P＜0.05 or P＜0.01）. The contraction rate could be increased by inhibiting inward rectifier potassium channels in vascular smooth muscle （P＜0.01）. Different dosages of psoralen and bakuchiol could significantly increase the expression levels of eNOS protein in rat cardiac microvascular endothelial cells（P＜0.01）. CONCLUSIONS： Psoralen and bakuchiol may play a role in vasodilation via endothelium-dependent NO pathway and by promoting eNOS protein expression in endothelial cells； bakuchiol may play a role in vasodilation via non-endothelium dependent pathway as opening inward rectifying potassium channel.