OBJECTIVE： To study the diastolic effect and mechanism of Hui medicine Hexin oil solution on isolated thoracic aortic vascular rings of rats， and provide reference for its treatment for cardiovascular diseases. METHODS： Thoracic aortic vascular rings of rats were taken and then soaked in Kelvin’s nutrient solution （K-H）. Using 1×10－6 mol/L norepinephrine （PE） or 60 mmol/L potassium chloride （KCl） for inducing the contraction of vascular rings， biological signal acquisition and analysis system was used to determine the diastolic effect and mechanism of Hexin oil solution with concentrations of 0.020 4， 0.040 8， 0.061 2， 0.081 6， 0.102 0 mg/mL on vascular rings， and diastolic rate was calculated. After culturing vascular rings by 0.1 mmol/L nitric oxide synthase inhibitor L-nitro-arginine methyl ester （L-NAME）， cyclooxygenase inhibitor indomethacin （INDO）， and potassium ion channel blocker glibenclamide （Gli） for 20 min， the diastolic effects of above-mentioned 5 mass concentrations of Hexin oil solution on the contraction of vascular rings pre-contracted by PE were determined， and diastolic rate was calculated. The test was based on K-H solution as blank control. RESULTS： Compared with blank control， Hexin oil solution with concentration of 0.020 4- 0.102 0 mg/mL had obvious diastolic effect on the contraction of vascular rings induced by PE and KCl （P＜0.05 or P＜0.01）， showing concentration-dependent relationship. INDO pre-treatment can relieve the diastolic effect of Hexin oil solution on vascular rings pre-contracted by PE； and compared with blank control group， the diastolic rate had no statistical significance （P＞0.05）. While the pre-treatment of Gli， L-NAME did not affect the diastolic effect of Hexin oil solution on vascular rings pre-contracted by PE； and compared with blank control group， diastolic rate was obviously increased （P＜0.05 or P＜0.01）. CONCLUSIONS： Hexin oil solution can concentration-dependently conduct the relaxation of thoracic aortic vascular rings pre-contracted by PE， KCl. The mechanism may be associated with activation of cyclooxygenase pathway.