Aim:Propyl gallate(PrG) is an artificially synthesized chemical which is an analog of ethyl gallate extracted from radices paeoniae rubra.Present study is to evaluate the vasorelaxant effect of PrG and its possible mechanism in isolated rat aortic rings.Methods:The vasorelaxant effect of PrG on rat aortic rings with or without endothelium pre-contracted by phenylephrine(PE) or KC1 was determined by isometric tension recording.N~G-nitro-L-arginine methyl ester(L-NAME),indomethacin and K~+ channel blockers were applied before aorta exposed to PrG.Ca~(2+) was been adding cumulatively in endothelium-denuded aorta in Ca~(2+) free K-H solution with PrG.Results:PrG ranged from 10 to 1000 M exerted a concentration-dependent relaxation on PE-pre-contracted rat aorta with or without endothelium.PrG at 1000M caused complete vascular relaxation in endothelium-intact or -denuded aortic rings.The pD_2 (-log IC_(50)) values of the vasorelaxant effect of PrG induced by PE for the endothelium-intact and -denuded aorta were 3.45±0.18 and 3.26±0.19 respectively, P＞0.05.Pretreated with L-NAME partially reversed the PrG-induced relaxation, pretreated with indomethacin had no observed effects.Pre-incubated with PrG(0,100, 300 and 1000 M) significantly inhibited the Ca~(2+)(10 mM) induced contraction in the Ca~(2+)-free Krebs in denuded rat aortic rings,the maximal contraction effect was 96.0±2.3%,81.1±2.5%,32.6±2.0%and 15.8±2.0%.K~+ channel blockers did not reversed vasorelaxation induced by PrG.Conclusion:PrG shows a concentration-dependent vasorelaxation on PE pre-contracted aortic rings in endothelium-dependent and -independent manner,and the mechanism of vasorelaxation of PrG is maybe through release of NO,inhibition of Ca~(2+) receptor and open of voltage channels.