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Abstract Background Vascular dysfunction can lead to many health problems including hypertension and heart disease. The complexities of vascular dysfunction and vascular disorder-related diseases have prompted the search for many new biologically active compounds in the efforts of resolving the problems. Previous studies have shown that Amaryllidaceae alkaloids exert multiple biological activities, including the vasorelaxation effect. Crinum amabile, which is a family member of Amaryllidaceae, is believed to possess a promising pharmacological activity as a vasorelaxant. Method The vasorelaxation activities of Crinum amabile extracts and fractions were determined using in vitro models of phenylephrine pre-contracted intact and denuded rat aortic rings. The mechanistic pathways of vasorelaxation were investigated by pre-treatment of endothelium-intact rat aortic rings with L-NG Nitro Arginine Methyl Ester (L-NAME), methylene blue (MB), indomethacin, atropine and propranolol, respectively. Results The results showed that chloroform extract (CE) of Crinum amabile exhibited the highest vasorelaxation activity, and further fractionation of CE found that its F5 fraction exerted the strongest activity. An in-depth study on the mechanistic pathway revealed that the endothelium-dependent vasorelaxation induced by F5 fraction was primarily achieved through stimulation of prostaglandin (PGI2) production and partially associated with NO/cGMP activation pathway. Conclusion Findings from this study suggest that Crinum amabile can serve as a promising candidate for the discovery and development of the new vasorelaxant drug.