Abstract: OBJECTIVE To investigate the effects and mechanisms of hawthorn flavonoids on vessel function in isolated rat aortic ring. METHODS To observe the effect of hawthorn flavonoids on isolated rat vascular diastolic and systolic function by building isolated rat vascular perfusion model. RESULTS Hawthorn flavonoids produced a dose-dependent vasodilation with or without endothelium. Pre-incubation with hawthorn flavonoids could inhibit vessel contraction induced by phenylephrine in a concentration-dependent way. Hawthorn flavonoids inhibited phenylephrine-induced and CaCl2-induced vasoconstriction in Ca2+-free medium. Pre-incubation with tetraethylammonium, a non-selective K+ channel blocker, and BaCl2, an inward rectifier K+ channel blocker, partially antagonized the relaxation response induced by hawthorn flavonoids. CONCLUSION Hawthorn flavonoids shows a endothelium-independent effect in isolated rat thoracic aortae mainly through blocking calcium influx and inhibiting intracellular calcium release, as well as opening non-selective K+ channel and inward rectifier K+ channel in the vascular smooth muscle cells.